Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.42   11.220%   $226.2437   $226.24   $226.25   $226.20  
  Purchase #2 $161.97   12.846%   $182.7767   $182.78   $182.80   $182.80  
  Purchase #3 $184.59   8.330%   $199.9663   $199.97   $199.95   $200.00  
  Purchase #4 $187.75   13.373%   $212.8578   $212.86   $212.85   $212.90  
  Purchase #5 $210.97   11.140%   $234.4721   $234.47   $234.45   $234.50  
  Purchase #6 $242.93   9.198%   $265.2747   $265.27   $265.25   $265.30  
  Purchase #7 $237.86   7.213%   $255.0168   $255.02   $255.00   $255.00  
  7 purchase totals = $1,429.49       $1,576.6081   $1,576.61   $1,576.55   $1,576.70