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 $229.92   9.444%   $251.6336   $251.63   $251.65   $251.60  
  Purchase #2 $29.94   8.562%   $32.5035   $32.50   $32.50   $32.50  
  Purchase #3 $182.93   13.581%   $207.7737   $207.77   $207.75   $207.80  
  Purchase #4 $58.61   9.729%   $64.3122   $64.31   $64.30   $64.30  
  Purchase #5 $208.63   11.685%   $233.0084   $233.01   $233.00   $233.00  
  Purchase #6 $171.78   5.312%   $180.905   $180.91   $180.90   $180.90  
  Purchase #7 $77.62   9.189%   $84.7525   $84.75   $84.75   $84.80  
  7 purchase totals = $959.43       $1,054.8889   $1,054.88   $1,054.85   $1,054.90