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 $57.60   8.119%   $62.2765   $62.28   $62.30   $62.30  
  Purchase #2 $49.40   8.401%   $53.5501   $53.55   $53.55   $53.60  
  Purchase #3 $43.57   8.352%   $47.209   $47.21   $47.20   $47.20  
  Purchase #4 $246.96   4.164%   $257.2434   $257.24   $257.25   $257.20  
  Purchase #5 $232.88   12.288%   $261.4963   $261.50   $261.50   $261.50  
  Purchase #6 $176.97   13.297%   $200.5017   $200.50   $200.50   $200.50  
  Purchase #7 $18.77   9.270%   $20.51   $20.51   $20.50   $20.50  
  7 purchase totals = $826.15       $902.7870   $902.79   $902.80   $902.80