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 $186.77   10.810%   $206.9598   $206.96   $206.95   $207.00  
  Purchase #2 $123.28   10.697%   $136.4673   $136.47   $136.45   $136.50  
  Purchase #3 $161.57   4.845%   $169.3981   $169.40   $169.40   $169.40  
  Purchase #4 $44.40   11.361%   $49.4443   $49.44   $49.45   $49.40  
  Purchase #5 $230.86   12.114%   $258.8264   $258.83   $258.85   $258.80  
  Purchase #6 $134.62   6.787%   $143.7567   $143.76   $143.75   $143.80  
  Purchase #7 $105.86   9.755%   $116.1866   $116.19   $116.20   $116.20  
  7 purchase totals = $987.36       $1,081.0392   $1,081.05   $1,081.05   $1,081.10