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 $196.51   10.557%   $217.2556   $217.26   $217.25   $217.30  
  Purchase #2 $75.46   5.149%   $79.3454   $79.35   $79.35   $79.30  
  Purchase #3 $170.33   8.598%   $184.975   $184.98   $185.00   $185.00  
  Purchase #4 $244.78   13.225%   $277.1522   $277.15   $277.15   $277.20  
  Purchase #5 $88.79   10.346%   $97.9762   $97.98   $98.00   $98.00  
  Purchase #6 $59.96   6.513%   $63.8652   $63.87   $63.85   $63.90  
  Purchase #7 $130.88   8.401%   $141.8752   $141.88   $141.90   $141.90  
  7 purchase totals = $966.71       $1,062.4448   $1,062.47   $1,062.50   $1,062.60