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 $81.93   13.426%   $92.9299   $92.93   $92.95   $92.90  
  Purchase #2 $236.93   8.620%   $257.3534   $257.35   $257.35   $257.40  
  Purchase #3 $228.30   6.185%   $242.4204   $242.42   $242.40   $242.40  
  Purchase #4 $100.25   12.534%   $112.8153   $112.82   $112.80   $112.80  
  Purchase #5 $182.75   8.730%   $198.7041   $198.70   $198.70   $198.70  
  Purchase #6 $246.64   3.376%   $254.9666   $254.97   $254.95   $255.00  
  Purchase #7 $129.77   3.731%   $134.6117   $134.61   $134.60   $134.60  
  7 purchase totals = $1,206.57       $1,293.8014   $1,293.80   $1,293.75   $1,293.80