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 $222.48   6.508%   $236.959   $236.96   $236.95   $237.00  
  Purchase #2 $163.85   5.812%   $173.373   $173.37   $173.35   $173.40  
  Purchase #3 $25.36   7.713%   $27.316   $27.32   $27.30   $27.30  
  Purchase #4 $53.52   4.130%   $55.7304   $55.73   $55.75   $55.70  
  Purchase #5 $214.71   5.683%   $226.912   $226.91   $226.90   $226.90  
  Purchase #6 $62.41   10.117%   $68.724   $68.72   $68.70   $68.70  
  Purchase #7 $22.79   12.774%   $25.7012   $25.70   $25.70   $25.70  
  7 purchase totals = $765.12       $814.7156   $814.71   $814.65   $814.70