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 $149.90   11.316%   $166.8627   $166.86   $166.85   $166.90  
  Purchase #2 $66.42   8.818%   $72.2769   $72.28   $72.30   $72.30  
  Purchase #3 $122.33   9.388%   $133.8143   $133.81   $133.80   $133.80  
  Purchase #4 $226.62   4.325%   $236.4213   $236.42   $236.40   $236.40  
  Purchase #5 $116.50   9.557%   $127.6339   $127.63   $127.65   $127.60  
  Purchase #6 $179.57   8.587%   $194.9897   $194.99   $195.00   $195.00  
  Purchase #7 $97.78   6.799%   $104.4281   $104.43   $104.45   $104.40  
  7 purchase totals = $959.12       $1,036.4269   $1,036.42   $1,036.45   $1,036.40