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 $184.99   8.122%   $200.0149   $200.01   $200.00   $200.00  
  Purchase #2 $49.62   4.405%   $51.8058   $51.81   $51.80   $51.80  
  Purchase #3 $59.60   11.505%   $66.457   $66.46   $66.45   $66.50  
  Purchase #4 $14.96   6.205%   $15.8883   $15.89   $15.90   $15.90  
  Purchase #5 $115.49   4.843%   $121.0832   $121.08   $121.10   $121.10  
  Purchase #6 $119.74   10.165%   $131.9116   $131.91   $131.90   $131.90  
  Purchase #7 $154.72   7.415%   $166.1925   $166.19   $166.20   $166.20  
  7 purchase totals = $699.12       $753.3533   $753.35   $753.35   $753.40