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 $37.36   10.740%   $41.3725   $41.37   $41.35   $41.40  
  Purchase #2 $231.44   12.662%   $260.7449   $260.74   $260.75   $260.70  
  Purchase #3 $18.47   5.530%   $19.4914   $19.49   $19.50   $19.50  
  Purchase #4 $147.69   13.302%   $167.3357   $167.34   $167.35   $167.30  
  Purchase #5 $60.77   11.525%   $67.7737   $67.77   $67.75   $67.80  
  Purchase #6 $193.98   5.213%   $204.0922   $204.09   $204.10   $204.10  
  Purchase #7 $154.67   7.196%   $165.8001   $165.80   $165.80   $165.80  
  7 purchase totals = $844.38       $926.6105   $926.60   $926.60   $926.60