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 $78.74   5.232%   $82.8597   $82.86   $82.85   $82.90  
  Purchase #2 $168.40   11.598%   $187.931   $187.93   $187.95   $187.90  
  Purchase #3 $68.71   12.194%   $77.0885   $77.09   $77.10   $77.10  
  Purchase #4 $30.88   12.458%   $34.727   $34.73   $34.75   $34.70  
  Purchase #5 $152.57   3.659%   $158.1525   $158.15   $158.15   $158.20  
  Purchase #6 $203.75   9.232%   $222.5602   $222.56   $222.55   $222.60  
  Purchase #7 $45.34   6.331%   $48.2105   $48.21   $48.20   $48.20  
  7 purchase totals = $748.39       $811.5294   $811.53   $811.55   $811.60