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 $59.91   12.164%   $67.1975   $67.20   $67.20   $67.20  
  Purchase #2 $174.33   13.813%   $198.4102   $198.41   $198.40   $198.40  
  Purchase #3 $104.80   7.232%   $112.3791   $112.38   $112.40   $112.40  
  Purchase #4 $245.99   5.354%   $259.1603   $259.16   $259.15   $259.20  
  Purchase #5 $76.48   9.562%   $83.793   $83.79   $83.80   $83.80  
  Purchase #6 $122.58   6.270%   $130.2658   $130.27   $130.25   $130.30  
  Purchase #7 $40.35   8.175%   $43.6486   $43.65   $43.65   $43.60  
  7 purchase totals = $824.44       $894.8545   $894.86   $894.85   $894.90