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 $57.44   6.159%   $60.9777   $60.98   $61.00   $61.00  
  Purchase #2 $51.83   6.405%   $55.1497   $55.15   $55.15   $55.10  
  Purchase #3 $116.32   11.335%   $129.5049   $129.50   $129.50   $129.50  
  Purchase #4 $148.73   8.869%   $161.9209   $161.92   $161.90   $161.90  
  Purchase #5 $63.71   11.519%   $71.0488   $71.05   $71.05   $71.00  
  Purchase #6 $129.72   11.472%   $144.6015   $144.60   $144.60   $144.60  
  Purchase #7 $241.59   12.176%   $271.006   $271.01   $271.00   $271.00  
  7 purchase totals = $809.34       $894.2095   $894.21   $894.20   $894.10