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 $249.49   12.709%   $281.1977   $281.20   $281.20   $281.20  
  Purchase #2 $105.99   6.275%   $112.6409   $112.64   $112.65   $112.60  
  Purchase #3 $212.70   10.586%   $235.2164   $235.22   $235.20   $235.20  
  Purchase #4 $100.95   7.757%   $108.7807   $108.78   $108.80   $108.80  
  Purchase #5 $200.60   11.438%   $223.5446   $223.54   $223.55   $223.50  
  Purchase #6 $209.69   11.543%   $233.8945   $233.89   $233.90   $233.90  
  Purchase #7 $44.59   8.478%   $48.3703   $48.37   $48.35   $48.40  
  7 purchase totals = $1,124.01       $1,243.6451   $1,243.64   $1,243.65   $1,243.60