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 $215.91   3.741%   $223.9872   $223.99   $224.00   $224.00  
  Purchase #2 $193.89   3.845%   $201.3451   $201.35   $201.35   $201.30  
  Purchase #3 $200.45   8.550%   $217.5885   $217.59   $217.60   $217.60  
  Purchase #4 $19.41   6.208%   $20.615   $20.62   $20.60   $20.60  
  Purchase #5 $85.82   10.511%   $94.8405   $94.84   $94.85   $94.80  
  Purchase #6 $182.88   4.108%   $190.3927   $190.39   $190.40   $190.40  
  Purchase #7 $48.85   13.453%   $55.4218   $55.42   $55.40   $55.40  
  7 purchase totals = $947.21       $1,004.1908   $1,004.20   $1,004.20   $1,004.10