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 $191.92   6.871%   $205.1068   $205.11   $205.10   $205.10  
  Purchase #2 $250.82   10.366%   $276.82   $276.82   $276.80   $276.80  
  Purchase #3 $178.85   13.667%   $203.2934   $203.29   $203.30   $203.30  
  Purchase #4 $112.80   12.201%   $126.5627   $126.56   $126.55   $126.60  
  Purchase #5 $236.82   6.378%   $251.9244   $251.92   $251.90   $251.90  
  Purchase #6 $114.82   4.387%   $119.8572   $119.86   $119.85   $119.90  
  Purchase #7 $184.97   7.452%   $198.754   $198.75   $198.75   $198.80  
  7 purchase totals = $1,271.00       $1,382.3185   $1,382.31   $1,382.25   $1,382.40