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 $108.74   9.778%   $119.3726   $119.37   $119.35   $119.40  
  Purchase #2 $186.75   3.435%   $193.1649   $193.16   $193.15   $193.20  
  Purchase #3 $137.87   3.242%   $142.3397   $142.34   $142.35   $142.30  
  Purchase #4 $202.35   8.481%   $219.5113   $219.51   $219.50   $219.50  
  Purchase #5 $32.32   4.393%   $33.7398   $33.74   $33.75   $33.70  
  Purchase #6 $163.68   9.593%   $179.3818   $179.38   $179.40   $179.40  
  Purchase #7 $239.84   5.382%   $252.7482   $252.75   $252.75   $252.70  
  7 purchase totals = $1,071.55       $1,140.2583   $1,140.25   $1,140.25   $1,140.20