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 $171.88   12.848%   $193.9631   $193.96   $193.95   $194.00  
  Purchase #2 $238.58   8.323%   $258.437   $258.44   $258.45   $258.40  
  Purchase #3 $246.26   3.578%   $255.0712   $255.07   $255.05   $255.10  
  Purchase #4 $189.86   8.730%   $206.4348   $206.43   $206.45   $206.40  
  Purchase #5 $141.68   11.533%   $158.02   $158.02   $158.00   $158.00  
  Purchase #6 $239.26   3.653%   $248.0002   $248.00   $248.00   $248.00  
  Purchase #7 $47.68   5.540%   $50.3215   $50.32   $50.30   $50.30  
  7 purchase totals = $1,275.20       $1,370.2478   $1,370.24   $1,370.20   $1,370.20