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 $77.56   6.525%   $82.6208   $82.62   $82.60   $82.60  
  Purchase #2 $206.98   9.328%   $226.2871   $226.29   $226.30   $226.30  
  Purchase #3 $65.42   7.846%   $70.5529   $70.55   $70.55   $70.60  
  Purchase #4 $236.61   8.729%   $257.2637   $257.26   $257.25   $257.30  
  Purchase #5 $74.64   8.704%   $81.1367   $81.14   $81.15   $81.10  
  Purchase #6 $87.68   10.633%   $97.003   $97.00   $97.00   $97.00  
  Purchase #7 $101.56   13.635%   $115.4077   $115.41   $115.40   $115.40  
  7 purchase totals = $850.45       $930.2719   $930.27   $930.25   $930.30