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 $40.85   5.282%   $43.0077   $43.01   $43.00   $43.00  
  Purchase #2 $55.26   13.455%   $62.6952   $62.70   $62.70   $62.70  
  Purchase #3 $114.92   12.226%   $128.9701   $128.97   $128.95   $129.00  
  Purchase #4 $98.97   7.698%   $106.5887   $106.59   $106.60   $106.60  
  Purchase #5 $243.60   12.143%   $273.1803   $273.18   $273.20   $273.20  
  Purchase #6 $154.41   4.684%   $161.6426   $161.64   $161.65   $161.60  
  Purchase #7 $24.41   7.809%   $26.3162   $26.32   $26.30   $26.30  
  7 purchase totals = $732.42       $802.4008   $802.41   $802.40   $802.40