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 $68.61   6.432%   $73.023   $73.02   $73.00   $73.00  
  Purchase #2 $246.69   5.226%   $259.582   $259.58   $259.60   $259.60  
  Purchase #3 $22.70   13.815%   $25.836   $25.84   $25.85   $25.80  
  Purchase #4 $158.98   3.483%   $164.5173   $164.52   $164.50   $164.50  
  Purchase #5 $221.51   5.644%   $234.012   $234.01   $234.00   $234.00  
  Purchase #6 $36.60   7.496%   $39.3435   $39.34   $39.35   $39.30  
  Purchase #7 $123.92   3.225%   $127.9164   $127.92   $127.90   $127.90  
  7 purchase totals = $879.01       $924.2302   $924.23   $924.20   $924.10