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 $113.94   4.240%   $118.7711   $118.77   $118.75   $118.80  
  Purchase #2 $186.83   10.757%   $206.9273   $206.93   $206.95   $206.90  
  Purchase #3 $95.45   8.434%   $103.5003   $103.50   $103.50   $103.50  
  Purchase #4 $143.73   11.104%   $159.6898   $159.69   $159.70   $159.70  
  Purchase #5 $158.89   8.137%   $171.8189   $171.82   $171.80   $171.80  
  Purchase #6 $8.25   3.511%   $8.5397   $8.54   $8.55   $8.50  
  Purchase #7 $172.59   9.626%   $189.2035   $189.20   $189.20   $189.20  
  7 purchase totals = $879.68       $958.4506   $958.45   $958.45   $958.40