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 $50.85   7.239%   $54.531   $54.53   $54.55   $54.50  
  Purchase #2 $232.84   8.774%   $253.2694   $253.27   $253.25   $253.30  
  Purchase #3 $111.92   13.241%   $126.7393   $126.74   $126.75   $126.70  
  Purchase #4 $204.40   11.619%   $228.1492   $228.15   $228.15   $228.10  
  Purchase #5 $177.96   12.246%   $199.753   $199.75   $199.75   $199.80  
  Purchase #6 $234.84   11.347%   $261.4873   $261.49   $261.50   $261.50  
  Purchase #7 $189.84   5.668%   $200.6001   $200.60   $200.60   $200.60  
  7 purchase totals = $1,202.65       $1,324.5293   $1,324.53   $1,324.55   $1,324.50