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 $60.83   10.520%   $67.2293   $67.23   $67.25   $67.20  
  Purchase #2 $121.74   8.871%   $132.5396   $132.54   $132.55   $132.50  
  Purchase #3 $130.82   3.439%   $135.3189   $135.32   $135.30   $135.30  
  Purchase #4 $72.81   3.607%   $75.4363   $75.44   $75.45   $75.40  
  Purchase #5 $125.32   8.449%   $135.9083   $135.91   $135.90   $135.90  
  Purchase #6 $114.82   12.780%   $129.494   $129.49   $129.50   $129.50  
  Purchase #7 $50.98   10.421%   $56.2926   $56.29   $56.30   $56.30  
  7 purchase totals = $677.32       $732.2190   $732.22   $732.25   $732.10