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 $238.26   5.692%   $251.8218   $251.82   $251.80   $251.80  
  Purchase #2 $113.41   4.594%   $118.6201   $118.62   $118.60   $118.60  
  Purchase #3 $37.58   6.580%   $40.0528   $40.05   $40.05   $40.10  
  Purchase #4 $71.51   13.815%   $81.3891   $81.39   $81.40   $81.40  
  Purchase #5 $248.34   5.125%   $261.0674   $261.07   $261.05   $261.10  
  Purchase #6 $58.62   6.226%   $62.2697   $62.27   $62.25   $62.30  
  Purchase #7 $166.67   12.620%   $187.7038   $187.70   $187.70   $187.70  
  7 purchase totals = $934.39       $1,002.9247   $1,002.92   $1,002.85   $1,003.00