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 $54.47   13.374%   $61.7548   $61.75   $61.75   $61.80  
  Purchase #2 $100.43   9.628%   $110.0994   $110.10   $110.10   $110.10  
  Purchase #3 $163.38   10.382%   $180.3421   $180.34   $180.35   $180.30  
  Purchase #4 $198.73   11.146%   $220.8804   $220.88   $220.90   $220.90  
  Purchase #5 $218.84   12.489%   $246.1709   $246.17   $246.15   $246.20  
  Purchase #6 $206.47   3.389%   $213.4673   $213.47   $213.45   $213.50  
  Purchase #7 $196.50   13.331%   $222.6954   $222.70   $222.70   $222.70  
  7 purchase totals = $1,138.82       $1,255.4103   $1,255.41   $1,255.40   $1,255.50