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 $58.88   9.627%   $64.5484   $64.55   $64.55   $64.50  
  Purchase #2 $235.41   12.684%   $265.2694   $265.27   $265.25   $265.30  
  Purchase #3 $229.85   9.605%   $251.9271   $251.93   $251.95   $251.90  
  Purchase #4 $32.47   10.438%   $35.8592   $35.86   $35.85   $35.90  
  Purchase #5 $175.36   11.605%   $195.7105   $195.71   $195.70   $195.70  
  Purchase #6 $197.70   6.206%   $209.9693   $209.97   $209.95   $210.00  
  Purchase #7 $28.45   6.418%   $30.2759   $30.28   $30.30   $30.30  
  7 purchase totals = $958.12       $1,053.5598   $1,053.57   $1,053.55   $1,053.60