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 $224.95   9.642%   $246.6397   $246.64   $246.65   $246.60  
  Purchase #2 $58.60   4.454%   $61.21   $61.21   $61.20   $61.20  
  Purchase #3 $52.99   5.435%   $55.87   $55.87   $55.85   $55.90  
  Purchase #4 $168.92   4.455%   $176.4454   $176.45   $176.45   $176.40  
  Purchase #5 $95.94   3.288%   $99.0945   $99.09   $99.10   $99.10  
  Purchase #6 $143.26   10.742%   $158.649   $158.65   $158.65   $158.60  
  Purchase #7 $249.77   4.434%   $260.8448   $260.84   $260.85   $260.80  
  7 purchase totals = $994.43       $1,058.7534   $1,058.75   $1,058.75   $1,058.60