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 $59.82   8.175%   $64.7103   $64.71   $64.70   $64.70  
  Purchase #2 $168.70   9.455%   $184.6506   $184.65   $184.65   $184.70  
  Purchase #3 $241.76   13.772%   $275.0552   $275.06   $275.05   $275.10  
  Purchase #4 $91.44   5.129%   $96.13   $96.13   $96.15   $96.10  
  Purchase #5 $144.79   8.615%   $157.2637   $157.26   $157.25   $157.30  
  Purchase #6 $40.59   11.713%   $45.3443   $45.34   $45.35   $45.30  
  Purchase #7 $41.47   9.176%   $45.2753   $45.28   $45.30   $45.30  
  7 purchase totals = $788.57       $868.4294   $868.43   $868.45   $868.50