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 $61.41   3.777%   $63.7295   $63.73   $63.75   $63.70  
  Purchase #2 $119.74   5.643%   $126.4969   $126.50   $126.50   $126.50  
  Purchase #3 $115.48   5.287%   $121.5854   $121.59   $121.60   $121.60  
  Purchase #4 $73.36   11.572%   $81.8492   $81.85   $81.85   $81.80  
  Purchase #5 $206.58   11.246%   $229.812   $229.81   $229.80   $229.80  
  Purchase #6 $203.39   4.203%   $211.9385   $211.94   $211.95   $211.90  
  Purchase #7 $183.93   11.377%   $204.8557   $204.86   $204.85   $204.90  
  7 purchase totals = $963.89       $1,040.2672   $1,040.28   $1,040.30   $1,040.20