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 $112.94   12.165%   $126.6792   $126.68   $126.70   $126.70  
  Purchase #2 $42.35   8.475%   $45.9392   $45.94   $45.95   $45.90  
  Purchase #3 $50.71   9.191%   $55.3708   $55.37   $55.35   $55.40  
  Purchase #4 $87.55   7.832%   $94.4069   $94.41   $94.40   $94.40  
  Purchase #5 $141.54   7.867%   $152.675   $152.68   $152.70   $152.70  
  Purchase #6 $119.41   5.537%   $126.0217   $126.02   $126.00   $126.00  
  Purchase #7 $243.67   6.198%   $258.7727   $258.77   $258.75   $258.80  
  7 purchase totals = $798.17       $859.8655   $859.87   $859.85   $859.90