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 $61.54   6.211%   $65.3622   $65.36   $65.35   $65.40  
  Purchase #2 $195.78   13.625%   $222.455   $222.46   $222.45   $222.50  
  Purchase #3 $109.68   8.707%   $119.2298   $119.23   $119.25   $119.20  
  Purchase #4 $189.57   5.848%   $200.6561   $200.66   $200.65   $200.70  
  Purchase #5 $87.66   7.422%   $94.1661   $94.17   $94.15   $94.20  
  Purchase #6 $46.46   11.756%   $51.9218   $51.92   $51.90   $51.90  
  Purchase #7 $11.26   5.159%   $11.8409   $11.84   $11.85   $11.80  
  7 purchase totals = $701.95       $765.6319   $765.64   $765.60   $765.70