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 $241.80   7.584%   $260.1381   $260.14   $260.15   $260.10  
  Purchase #2 $116.88   3.478%   $120.9451   $120.95   $120.95   $120.90  
  Purchase #3 $202.47   9.683%   $222.0752   $222.08   $222.10   $222.10  
  Purchase #4 $175.29   11.601%   $195.6254   $195.63   $195.65   $195.60  
  Purchase #5 $173.94   5.104%   $182.8179   $182.82   $182.80   $182.80  
  Purchase #6 $17.30   11.271%   $19.2499   $19.25   $19.25   $19.20  
  Purchase #7 $12.47   12.874%   $14.0754   $14.08   $14.10   $14.10  
  7 purchase totals = $940.15       $1,014.9270   $1,014.95   $1,015.00   $1,014.80