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 $32.28   12.368%   $36.2724   $36.27   $36.25   $36.30  
  Purchase #2 $216.65   8.816%   $235.7499   $235.75   $235.75   $235.70  
  Purchase #3 $105.70   12.552%   $118.9675   $118.97   $118.95   $119.00  
  Purchase #4 $33.36   4.770%   $34.9513   $34.95   $34.95   $35.00  
  Purchase #5 $236.73   12.360%   $265.9898   $265.99   $266.00   $266.00  
  Purchase #6 $231.47   5.735%   $244.7448   $244.74   $244.75   $244.70  
  Purchase #7 $78.65   9.268%   $85.9393   $85.94   $85.95   $85.90  
  7 purchase totals = $934.84       $1,022.6150   $1,022.61   $1,022.60   $1,022.60