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 $198.71   4.417%   $207.487   $207.49   $207.50   $207.50  
  Purchase #2 $48.53   8.279%   $52.5478   $52.55   $52.55   $52.50  
  Purchase #3 $68.60   11.423%   $76.4362   $76.44   $76.45   $76.40  
  Purchase #4 $67.51   7.532%   $72.5949   $72.59   $72.60   $72.60  
  Purchase #5 $53.31   8.693%   $57.9442   $57.94   $57.95   $57.90  
  Purchase #6 $172.61   5.616%   $182.3038   $182.30   $182.30   $182.30  
  Purchase #7 $129.82   11.699%   $145.0076   $145.01   $145.00   $145.00  
  7 purchase totals = $739.09       $794.3215   $794.32   $794.35   $794.20