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 $70.25   4.601%   $73.4822   $73.48   $73.50   $73.50  
  Purchase #2 $234.33   5.804%   $247.9305   $247.93   $247.95   $247.90  
  Purchase #3 $214.27   11.361%   $238.6132   $238.61   $238.60   $238.60  
  Purchase #4 $148.70   9.576%   $162.9395   $162.94   $162.95   $162.90  
  Purchase #5 $62.59   10.132%   $68.9316   $68.93   $68.95   $68.90  
  Purchase #6 $241.45   3.685%   $250.3474   $250.35   $250.35   $250.30  
  Purchase #7 $201.41   12.763%   $227.116   $227.12   $227.10   $227.10  
  7 purchase totals = $1,173.00       $1,269.3604   $1,269.36   $1,269.40   $1,269.20