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 $85.53   12.698%   $96.3906   $96.39   $96.40   $96.40  
  Purchase #2 $81.37   11.372%   $90.6234   $90.62   $90.60   $90.60  
  Purchase #3 $225.26   13.375%   $255.3885   $255.39   $255.40   $255.40  
  Purchase #4 $124.89   8.777%   $135.8516   $135.85   $135.85   $135.90  
  Purchase #5 $218.76   10.436%   $241.5898   $241.59   $241.60   $241.60  
  Purchase #6 $51.49   10.198%   $56.741   $56.74   $56.75   $56.70  
  Purchase #7 $71.27   6.814%   $76.1263   $76.13   $76.15   $76.10  
  7 purchase totals = $858.57       $952.7112   $952.71   $952.75   $952.70