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 $215.76   10.492%   $238.3975   $238.40   $238.40   $238.40  
  Purchase #2 $177.75   7.626%   $191.3052   $191.31   $191.30   $191.30  
  Purchase #3 $53.75   11.624%   $59.9979   $60.00   $60.00   $60.00  
  Purchase #4 $139.92   10.331%   $154.3751   $154.38   $154.40   $154.40  
  Purchase #5 $230.93   8.244%   $249.9679   $249.97   $249.95   $250.00  
  Purchase #6 $195.42   9.579%   $214.1393   $214.14   $214.15   $214.10  
  Purchase #7 $108.53   8.284%   $117.5206   $117.52   $117.50   $117.50  
  7 purchase totals = $1,122.06       $1,225.7035   $1,225.72   $1,225.70   $1,225.70