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 $85.92   9.424%   $94.0171   $94.02   $94.00   $94.00  
  Purchase #2 $144.78   5.417%   $152.6227   $152.62   $152.60   $152.60  
  Purchase #3 $214.74   6.779%   $229.2972   $229.30   $229.30   $229.30  
  Purchase #4 $46.47   9.512%   $50.8902   $50.89   $50.90   $50.90  
  Purchase #5 $168.77   7.644%   $181.6708   $181.67   $181.65   $181.70  
  Purchase #6 $127.44   11.404%   $141.9733   $141.97   $141.95   $142.00  
  Purchase #7 $182.73   4.589%   $191.1155   $191.12   $191.10   $191.10  
  7 purchase totals = $970.85       $1,041.5868   $1,041.59   $1,041.50   $1,041.60