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 $78.71   11.682%   $87.9049   $87.90   $87.90   $87.90  
  Purchase #2 $175.63   11.491%   $195.8116   $195.81   $195.80   $195.80  
  Purchase #3 $61.29   7.445%   $65.853   $65.85   $65.85   $65.90  
  Purchase #4 $163.95   5.204%   $172.482   $172.48   $172.50   $172.50  
  Purchase #5 $131.86   3.654%   $136.6782   $136.68   $136.70   $136.70  
  Purchase #6 $185.40   10.605%   $205.0617   $205.06   $205.05   $205.10  
  Purchase #7 $239.81   5.551%   $253.1219   $253.12   $253.10   $253.10  
  7 purchase totals = $1,036.65       $1,116.9133   $1,116.90   $1,116.90   $1,117.00