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 $96.52   8.400%   $104.6277   $104.63   $104.65   $104.60  
  Purchase #2 $91.94   8.382%   $99.6464   $99.65   $99.65   $99.60  
  Purchase #3 $121.69   8.683%   $132.2563   $132.26   $132.25   $132.30  
  Purchase #4 $131.98   8.338%   $142.9845   $142.98   $143.00   $143.00  
  Purchase #5 $239.88   5.873%   $253.9682   $253.97   $253.95   $254.00  
  Purchase #6 $89.62   9.511%   $98.1438   $98.14   $98.15   $98.10  
  Purchase #7 $188.50   13.669%   $214.2661   $214.27   $214.25   $214.30  
  7 purchase totals = $960.13       $1,045.8930   $1,045.90   $1,045.90   $1,045.90