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 $66.73   9.762%   $73.2442   $73.24   $73.25   $73.20  
  Purchase #2 $22.57   12.352%   $25.3578   $25.36   $25.35   $25.40  
  Purchase #3 $88.39   12.683%   $99.6005   $99.60   $99.60   $99.60  
  Purchase #4 $206.49   13.636%   $234.647   $234.65   $234.65   $234.60  
  Purchase #5 $100.84   4.636%   $105.5149   $105.51   $105.50   $105.50  
  Purchase #6 $187.41   13.687%   $213.0608   $213.06   $213.05   $213.10  
  Purchase #7 $217.59   6.773%   $232.3274   $232.33   $232.35   $232.30  
  7 purchase totals = $890.02       $983.7526   $983.75   $983.75   $983.70