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 $211.69   11.795%   $236.6588   $236.66   $236.65   $236.70  
  Purchase #2 $218.85   9.189%   $238.9601   $238.96   $238.95   $239.00  
  Purchase #3 $32.47   13.147%   $36.7388   $36.74   $36.75   $36.70  
  Purchase #4 $91.57   8.730%   $99.5641   $99.56   $99.55   $99.60  
  Purchase #5 $78.63   10.242%   $86.6833   $86.68   $86.70   $86.70  
  Purchase #6 $173.60   12.163%   $194.715   $194.72   $194.70   $194.70  
  Purchase #7 $87.94   3.276%   $90.8209   $90.82   $90.80   $90.80  
  7 purchase totals = $894.75       $984.1410   $984.14   $984.10   $984.20