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 $216.63   8.218%   $234.4327   $234.43   $234.45   $234.40  
  Purchase #2 $93.98   7.601%   $101.1234   $101.12   $101.10   $101.10  
  Purchase #3 $166.32   8.459%   $180.389   $180.39   $180.40   $180.40  
  Purchase #4 $199.96   10.277%   $220.5099   $220.51   $220.50   $220.50  
  Purchase #5 $186.71   3.522%   $193.2859   $193.29   $193.30   $193.30  
  Purchase #6 $209.27   4.679%   $219.0617   $219.06   $219.05   $219.10  
  Purchase #7 $127.31   4.644%   $133.2223   $133.22   $133.20   $133.20  
  7 purchase totals = $1,200.18       $1,282.0249   $1,282.02   $1,282.00   $1,282.00