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 $97.68   7.266%   $104.7774   $104.78   $104.80   $104.80  
  Purchase #2 $182.86   4.345%   $190.8053   $190.81   $190.80   $190.80  
  Purchase #3 $33.43   4.780%   $35.028   $35.03   $35.05   $35.00  
  Purchase #4 $243.63   8.212%   $263.6369   $263.64   $263.65   $263.60  
  Purchase #5 $127.53   5.864%   $135.0084   $135.01   $135.00   $135.00  
  Purchase #6 $113.67   13.786%   $129.3405   $129.34   $129.35   $129.30  
  Purchase #7 $96.84   6.260%   $102.9022   $102.90   $102.90   $102.90  
  7 purchase totals = $895.64       $961.4987   $961.51   $961.55   $961.40