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 $60.97   3.622%   $63.1783   $63.18   $63.20   $63.20  
  Purchase #2 $102.72   12.645%   $115.7089   $115.71   $115.70   $115.70  
  Purchase #3 $169.35   8.136%   $183.1283   $183.13   $183.15   $183.10  
  Purchase #4 $213.56   6.223%   $226.8498   $226.85   $226.85   $226.80  
  Purchase #5 $9.26   12.379%   $10.4063   $10.41   $10.40   $10.40  
  Purchase #6 $235.57   4.711%   $246.6677   $246.67   $246.65   $246.70  
  Purchase #7 $135.94   4.221%   $141.678   $141.68   $141.70   $141.70  
  7 purchase totals = $927.37       $987.6173   $987.63   $987.65   $987.60