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 $56.70   11.698%   $63.3328   $63.33   $63.35   $63.30  
  Purchase #2 $216.82   9.432%   $237.2705   $237.27   $237.25   $237.30  
  Purchase #3 $81.34   8.680%   $88.4003   $88.40   $88.40   $88.40  
  Purchase #4 $165.89   5.328%   $174.7286   $174.73   $174.75   $174.70  
  Purchase #5 $207.67   13.492%   $235.6888   $235.69   $235.70   $235.70  
  Purchase #6 $44.76   8.324%   $48.4858   $48.49   $48.50   $48.50  
  Purchase #7 $108.30   3.859%   $112.4793   $112.48   $112.50   $112.50  
  7 purchase totals = $881.48       $960.3861   $960.39   $960.45   $960.40