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 $185.34   10.306%   $204.4411   $204.44   $204.45   $204.40  
  Purchase #2 $126.80   13.297%   $143.6606   $143.66   $143.65   $143.70  
  Purchase #3 $54.62   9.762%   $59.952   $59.95   $59.95   $60.00  
  Purchase #4 $214.64   11.752%   $239.8645   $239.86   $239.85   $239.90  
  Purchase #5 $155.83   13.657%   $177.1117   $177.11   $177.10   $177.10  
  Purchase #6 $40.55   7.280%   $43.502   $43.50   $43.50   $43.50  
  Purchase #7 $93.46   4.211%   $97.3956   $97.40   $97.40   $97.40  
  7 purchase totals = $871.24       $965.9275   $965.92   $965.90   $966.00