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 $49.42   7.208%   $52.9822   $52.98   $53.00   $53.00  
  Purchase #2 $215.74   9.171%   $235.5255   $235.53   $235.55   $235.50  
  Purchase #3 $180.83   7.293%   $194.0179   $194.02   $194.00   $194.00  
  Purchase #4 $216.73   3.588%   $224.5063   $224.51   $224.50   $224.50  
  Purchase #5 $9.88   11.274%   $10.9939   $10.99   $11.00   $11.00  
  Purchase #6 $249.74   4.573%   $261.1606   $261.16   $261.15   $261.20  
  Purchase #7 $26.67   4.588%   $27.8936   $27.89   $27.90   $27.90  
  7 purchase totals = $949.01       $1,007.0800   $1,007.08   $1,007.10   $1,007.10