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 $217.67   10.549%   $240.632   $240.63   $240.65   $240.60  
  Purchase #2 $105.62   10.284%   $116.482   $116.48   $116.50   $116.50  
  Purchase #3 $211.54   8.517%   $229.5569   $229.56   $229.55   $229.60  
  Purchase #4 $241.49   10.643%   $267.1918   $267.19   $267.20   $267.20  
  Purchase #5 $81.28   8.698%   $88.3497   $88.35   $88.35   $88.30  
  Purchase #6 $228.86   11.441%   $255.0439   $255.04   $255.05   $255.00  
  Purchase #7 $235.67   11.189%   $262.0391   $262.04   $262.05   $262.00  
  7 purchase totals = $1,322.13       $1,459.2954   $1,459.29   $1,459.35   $1,459.20