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 $222.25   3.764%   $230.6155   $230.62   $230.60   $230.60  
  Purchase #2 $87.29   10.316%   $96.2948   $96.29   $96.30   $96.30  
  Purchase #3 $158.63   3.702%   $164.5025   $164.50   $164.50   $164.50  
  Purchase #4 $250.97   8.144%   $271.409   $271.41   $271.40   $271.40  
  Purchase #5 $241.80   6.352%   $257.1591   $257.16   $257.15   $257.20  
  Purchase #6 $196.49   12.375%   $220.8056   $220.81   $220.80   $220.80  
  Purchase #7 $157.91   9.753%   $173.311   $173.31   $173.30   $173.30  
  7 purchase totals = $1,315.34       $1,414.0975   $1,414.10   $1,414.05   $1,414.10