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 $214.26   11.629%   $239.1763   $239.18   $239.20   $239.20  
  Purchase #2 $90.54   4.822%   $94.9058   $94.91   $94.90   $94.90  
  Purchase #3 $43.73   12.778%   $49.3178   $49.32   $49.30   $49.30  
  Purchase #4 $126.61   11.491%   $141.1588   $141.16   $141.15   $141.20  
  Purchase #5 $222.85   5.674%   $235.4945   $235.49   $235.50   $235.50  
  Purchase #6 $145.53   3.707%   $150.9248   $150.92   $150.90   $150.90  
  Purchase #7 $48.50   13.415%   $55.0063   $55.01   $55.00   $55.00  
  7 purchase totals = $892.02       $965.9843   $965.99   $965.95   $966.00