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 $66.86   11.678%   $74.6679   $74.67   $74.65   $74.70  
  Purchase #2 $144.63   9.519%   $158.3973   $158.40   $158.40   $158.40  
  Purchase #3 $143.64   13.210%   $162.6148   $162.61   $162.60   $162.60  
  Purchase #4 $159.94   11.164%   $177.7957   $177.80   $177.80   $177.80  
  Purchase #5 $119.95   13.114%   $135.6802   $135.68   $135.70   $135.70  
  Purchase #6 $92.37   4.714%   $96.7243   $96.72   $96.70   $96.70  
  Purchase #7 $160.38   12.767%   $180.8557   $180.86   $180.85   $180.90  
  7 purchase totals = $887.77       $986.7359   $986.74   $986.70   $986.80