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	$130.79	8.581%	$142.0131	$142.01	$142.00	$142.00
Purchase #2	$172.99	7.279%	$185.5819	$185.58	$185.60	$185.60
Purchase #3	$18.91	12.539%	$21.2811	$21.28	$21.30	$21.30
Purchase #4	$249.88	13.791%	$284.341	$284.34	$284.35	$284.30
Purchase #5	$98.51	12.862%	$111.1804	$111.18	$111.20	$111.20
Purchase #6	$157.57	4.517%	$164.6874	$164.69	$164.70	$164.70
Purchase #7	$81.44	8.804%	$88.61	$88.61	$88.60	$88.60
7 purchase totals =	$910.09		$997.6949	$997.69	$997.75	$997.70