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 $37.68   11.362%   $41.9612   $41.96   $41.95   $42.00  
  Purchase #2 $206.44   9.215%   $225.4634   $225.46   $225.45   $225.50  
  Purchase #3 $112.72   11.803%   $126.0243   $126.02   $126.00   $126.00  
  Purchase #4 $173.33   3.576%   $179.5283   $179.53   $179.55   $179.50  
  Purchase #5 $151.49   3.160%   $156.2771   $156.28   $156.30   $156.30  
  Purchase #6 $117.35   7.873%   $126.589   $126.59   $126.60   $126.60  
  Purchase #7 $74.36   7.166%   $79.6886   $79.69   $79.70   $79.70  
  7 purchase totals = $873.37       $935.5319   $935.53   $935.55   $935.60