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 $48.71   8.201%   $52.7047   $52.70   $52.70   $52.70  
  Purchase #2 $205.45   9.649%   $225.2739   $225.27   $225.25   $225.30  
  Purchase #3 $199.49   12.177%   $223.7819   $223.78   $223.80   $223.80  
  Purchase #4 $221.59   9.400%   $242.4195   $242.42   $242.40   $242.40  
  Purchase #5 $168.77   7.408%   $181.2725   $181.27   $181.25   $181.30  
  Purchase #6 $198.32   8.741%   $215.6552   $215.66   $215.65   $215.70  
  Purchase #7 $172.72   13.136%   $195.4085   $195.41   $195.40   $195.40  
  7 purchase totals = $1,215.05       $1,336.5162   $1,336.51   $1,336.45   $1,336.60