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 $244.44   6.863%   $261.2159   $261.22   $261.20   $261.20  
  Purchase #2 $63.46   8.209%   $68.6694   $68.67   $68.65   $68.70  
  Purchase #3 $243.74   11.792%   $272.4818   $272.48   $272.50   $272.50  
  Purchase #4 $208.48   7.567%   $224.2557   $224.26   $224.25   $224.30  
  Purchase #5 $68.50   9.299%   $74.8698   $74.87   $74.85   $74.90  
  Purchase #6 $60.33   12.797%   $68.0504   $68.05   $68.05   $68.10  
  Purchase #7 $57.84   5.199%   $60.8471   $60.85   $60.85   $60.80  
  7 purchase totals = $946.79       $1,030.3901   $1,030.40   $1,030.35   $1,030.50