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 $153.38   8.243%   $166.0231   $166.02   $166.00   $166.00  
  Purchase #2 $232.90   7.285%   $249.8668   $249.87   $249.85   $249.90  
  Purchase #3 $34.66   4.667%   $36.2776   $36.28   $36.30   $36.30  
  Purchase #4 $225.78   6.102%   $239.5571   $239.56   $239.55   $239.60  
  Purchase #5 $50.68   9.507%   $55.4981   $55.50   $55.50   $55.50  
  Purchase #6 $68.74   9.197%   $75.062   $75.06   $75.05   $75.10  
  Purchase #7 $128.52   3.118%   $132.5273   $132.53   $132.55   $132.50  
  7 purchase totals = $894.66       $954.8120   $954.82   $954.80   $954.90