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 $104.83   13.106%   $118.569   $118.57   $118.55   $118.60  
  Purchase #2 $168.54   8.179%   $182.3249   $182.32   $182.30   $182.30  
  Purchase #3 $188.95   13.357%   $214.1881   $214.19   $214.20   $214.20  
  Purchase #4 $94.51   10.228%   $104.1765   $104.18   $104.20   $104.20  
  Purchase #5 $70.54   7.768%   $76.0195   $76.02   $76.00   $76.00  
  Purchase #6 $231.43   5.539%   $244.2489   $244.25   $244.25   $244.20  
  Purchase #7 $26.49   12.269%   $29.7401   $29.74   $29.75   $29.70  
  7 purchase totals = $885.29       $969.2670   $969.27   $969.25   $969.20