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 $171.96   13.655%   $195.4411   $195.44   $195.45   $195.40  
  Purchase #2 $130.94   3.669%   $135.7442   $135.74   $135.75   $135.70  
  Purchase #3 $103.46   4.167%   $107.7712   $107.77   $107.75   $107.80  
  Purchase #4 $126.79   8.372%   $137.4049   $137.40   $137.40   $137.40  
  Purchase #5 $151.66   8.707%   $164.865   $164.87   $164.85   $164.90  
  Purchase #6 $123.83   6.176%   $131.4777   $131.48   $131.50   $131.50  
  Purchase #7 $69.98   9.370%   $76.5371   $76.54   $76.55   $76.50  
  7 purchase totals = $878.62       $949.2412   $949.24   $949.25   $949.20