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 $207.33   5.273%   $218.2625   $218.26   $218.25   $218.30  
  Purchase #2 $83.27   11.448%   $92.8027   $92.80   $92.80   $92.80  
  Purchase #3 $249.75   4.546%   $261.1036   $261.10   $261.10   $261.10  
  Purchase #4 $225.86   11.385%   $251.5742   $251.57   $251.55   $251.60  
  Purchase #5 $49.48   5.475%   $52.189   $52.19   $52.20   $52.20  
  Purchase #6 $64.94   5.137%   $68.276   $68.28   $68.30   $68.30  
  Purchase #7 $10.66   11.484%   $11.8842   $11.88   $11.90   $11.90  
  7 purchase totals = $891.29       $956.0922   $956.08   $956.10   $956.20