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 $46.95   12.505%   $52.8211   $52.82   $52.80   $52.80  
  Purchase #2 $54.47   5.368%   $57.3939   $57.39   $57.40   $57.40  
  Purchase #3 $12.98   11.741%   $14.504   $14.50   $14.50   $14.50  
  Purchase #4 $178.33   11.350%   $198.5705   $198.57   $198.55   $198.60  
  Purchase #5 $124.61   6.691%   $132.9477   $132.95   $132.95   $132.90  
  Purchase #6 $240.78   8.345%   $260.8731   $260.87   $260.85   $260.90  
  Purchase #7 $123.38   11.624%   $137.7217   $137.72   $137.70   $137.70  
  7 purchase totals = $781.50       $854.8320   $854.82   $854.75   $854.80