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 $192.41   8.140%   $208.0722   $208.07   $208.05   $208.10  
  Purchase #2 $242.82   11.659%   $271.1304   $271.13   $271.15   $271.10  
  Purchase #3 $150.49   11.555%   $167.8791   $167.88   $167.90   $167.90  
  Purchase #4 $80.79   13.554%   $91.7403   $91.74   $91.75   $91.70  
  Purchase #5 $5.96   10.547%   $6.5886   $6.59   $6.60   $6.60  
  Purchase #6 $197.57   10.243%   $217.8071   $217.81   $217.80   $217.80  
  Purchase #7 $27.64   10.385%   $30.5104   $30.51   $30.50   $30.50  
  7 purchase totals = $897.68       $993.7281   $993.73   $993.75   $993.70