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 $194.68   12.771%   $219.5426   $219.54   $219.55   $219.50  
  Purchase #2 $240.51   4.312%   $250.8808   $250.88   $250.90   $250.90  
  Purchase #3 $209.41   5.817%   $221.5914   $221.59   $221.60   $221.60  
  Purchase #4 $156.26   4.696%   $163.598   $163.60   $163.60   $163.60  
  Purchase #5 $158.58   12.689%   $178.7022   $178.70   $178.70   $178.70  
  Purchase #6 $162.81   11.134%   $180.9373   $180.94   $180.95   $180.90  
  Purchase #7 $178.88   10.544%   $197.7411   $197.74   $197.75   $197.70  
  7 purchase totals = $1,301.13       $1,412.9934   $1,412.99   $1,413.05   $1,412.90