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 $186.56   12.140%   $209.2084   $209.21   $209.20   $209.20  
  Purchase #2 $197.95   5.821%   $209.4727   $209.47   $209.45   $209.50  
  Purchase #3 $20.88   12.293%   $23.4468   $23.45   $23.45   $23.40  
  Purchase #4 $49.69   4.153%   $51.7536   $51.75   $51.75   $51.80  
  Purchase #5 $206.37   5.862%   $218.4674   $218.47   $218.45   $218.50  
  Purchase #6 $23.76   5.139%   $24.981   $24.98   $25.00   $25.00  
  Purchase #7 $81.93   4.598%   $85.6971   $85.70   $85.70   $85.70  
  7 purchase totals = $767.14       $823.0270   $823.03   $823.00   $823.10