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 $45.31   9.807%   $49.7536   $49.75   $49.75   $49.80  
  Purchase #2 $59.73   12.598%   $67.2548   $67.25   $67.25   $67.30  
  Purchase #3 $54.95   5.320%   $57.8733   $57.87   $57.85   $57.90  
  Purchase #4 $54.57   11.334%   $60.755   $60.76   $60.75   $60.80  
  Purchase #5 $95.38   9.740%   $104.67   $104.67   $104.65   $104.70  
  Purchase #6 $175.74   12.488%   $197.6864   $197.69   $197.70   $197.70  
  Purchase #7 $59.78   7.347%   $64.172   $64.17   $64.15   $64.20  
  7 purchase totals = $545.46       $602.1651   $602.16   $602.10   $602.40