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 $249.39   6.416%   $265.3909   $265.39   $265.40   $265.40  
  Purchase #2 $41.77   10.599%   $46.1972   $46.20   $46.20   $46.20  
  Purchase #3 $243.25   12.227%   $272.9922   $272.99   $273.00   $273.00  
  Purchase #4 $209.55   3.714%   $217.3327   $217.33   $217.35   $217.30  
  Purchase #5 $113.87   9.490%   $124.6763   $124.68   $124.70   $124.70  
  Purchase #6 $18.30   3.527%   $18.9454   $18.95   $18.95   $18.90  
  Purchase #7 $115.94   9.113%   $126.5056   $126.51   $126.50   $126.50  
  7 purchase totals = $992.07       $1,072.0403   $1,072.05   $1,072.10   $1,072.00