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	$8.35	6.687%	$8.9084	$8.91	$8.90	$8.90
Purchase #2	$236.50	5.726%	$250.042	$250.04	$250.05	$250.00
Purchase #3	$194.45	10.767%	$215.3864	$215.39	$215.40	$215.40
Purchase #4	$7.26	13.463%	$8.2374	$8.24	$8.25	$8.20
Purchase #5	$31.89	10.755%	$35.3198	$35.32	$35.30	$35.30
Purchase #6	$75.77	4.105%	$78.8804	$78.88	$78.90	$78.90
Purchase #7	$40.73	10.864%	$45.1549	$45.15	$45.15	$45.20
7 purchase totals =	$594.95		$641.9293	$641.93	$641.95	$641.90