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 $201.42   8.494%   $218.5286   $218.53   $218.55   $218.50  
  Purchase #2 $131.84   7.402%   $141.5988   $141.60   $141.60   $141.60  
  Purchase #3 $245.60   6.119%   $260.6283   $260.63   $260.65   $260.60  
  Purchase #4 $177.65   13.417%   $201.4853   $201.49   $201.50   $201.50  
  Purchase #5 $236.78   11.104%   $263.0721   $263.07   $263.05   $263.10  
  Purchase #6 $59.58   10.743%   $65.9807   $65.98   $66.00   $66.00  
  Purchase #7 $108.98   6.482%   $116.0441   $116.04   $116.05   $116.00  
  7 purchase totals = $1,161.85       $1,267.3379   $1,267.34   $1,267.40   $1,267.30