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 $241.96   3.176%   $249.6446   $249.64   $249.65   $249.60  
  Purchase #2 $8.94   13.201%   $10.1202   $10.12   $10.10   $10.10  
  Purchase #3 $194.77   3.212%   $201.026   $201.03   $201.05   $201.00  
  Purchase #4 $84.80   9.122%   $92.5355   $92.54   $92.55   $92.50  
  Purchase #5 $98.44   8.329%   $106.6391   $106.64   $106.65   $106.60  
  Purchase #6 $108.26   8.201%   $117.1384   $117.14   $117.15   $117.10  
  Purchase #7 $158.62   8.244%   $171.6966   $171.70   $171.70   $171.70  
  7 purchase totals = $895.79       $948.8004   $948.81   $948.85   $948.60