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 $69.74   9.467%   $76.3423   $76.34   $76.35   $76.30  
  Purchase #2 $237.71   12.291%   $266.9269   $266.93   $266.95   $266.90  
  Purchase #3 $196.75   4.681%   $205.9599   $205.96   $205.95   $206.00  
  Purchase #4 $78.67   6.753%   $83.9826   $83.98   $84.00   $84.00  
  Purchase #5 $153.36   3.763%   $159.1309   $159.13   $159.15   $159.10  
  Purchase #6 $9.95   8.392%   $10.785   $10.79   $10.80   $10.80  
  Purchase #7 $205.65   4.435%   $214.7706   $214.77   $214.75   $214.80  
  7 purchase totals = $951.83       $1,017.8982   $1,017.90   $1,017.95   $1,017.90