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 $56.42   12.463%   $63.4516   $63.45   $63.45   $63.50  
  Purchase #2 $195.72   11.221%   $217.6817   $217.68   $217.70   $217.70  
  Purchase #3 $24.60   13.112%   $27.8256   $27.83   $27.85   $27.80  
  Purchase #4 $108.63   5.683%   $114.8034   $114.80   $114.80   $114.80  
  Purchase #5 $167.88   6.313%   $178.4783   $178.48   $178.50   $178.50  
  Purchase #6 $146.88   6.677%   $156.6872   $156.69   $156.70   $156.70  
  Purchase #7 $44.68   7.747%   $48.1414   $48.14   $48.15   $48.10  
  7 purchase totals = $744.81       $807.0692   $807.07   $807.15   $807.10