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 $98.94   3.400%   $102.304   $102.30   $102.30   $102.30  
  Purchase #2 $121.77   13.200%   $137.8436   $137.84   $137.85   $137.80  
  Purchase #3 $137.62   5.313%   $144.9318   $144.93   $144.95   $144.90  
  Purchase #4 $115.66   12.800%   $130.4645   $130.46   $130.45   $130.50  
  Purchase #5 $70.55   6.676%   $75.2599   $75.26   $75.25   $75.30  
  Purchase #6 $107.53   5.497%   $113.4409   $113.44   $113.45   $113.40  
  Purchase #7 $122.56   5.606%   $129.4307   $129.43   $129.45   $129.40  
  7 purchase totals = $774.63       $833.6754   $833.66   $833.70   $833.60