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 $45.92   8.657%   $49.8953   $49.90   $49.90   $49.90  
  Purchase #2 $104.63   8.541%   $113.5664   $113.57   $113.55   $113.60  
  Purchase #3 $156.40   12.398%   $175.7905   $175.79   $175.80   $175.80  
  Purchase #4 $92.75   5.618%   $97.9607   $97.96   $97.95   $98.00  
  Purchase #5 $86.35   9.490%   $94.5446   $94.54   $94.55   $94.50  
  Purchase #6 $222.96   7.103%   $238.7968   $238.80   $238.80   $238.80  
  Purchase #7 $117.69   6.584%   $125.4387   $125.44   $125.45   $125.40  
  7 purchase totals = $826.70       $895.9930   $896.00   $896.00   $896.00