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	$37.51	4.742%	$39.2887	$39.29	$39.30	$39.30
Purchase #2	$151.31	12.682%	$170.4991	$170.50	$170.50	$170.50
Purchase #3	$90.67	6.471%	$96.5373	$96.54	$96.55	$96.50
Purchase #4	$249.39	6.703%	$266.1066	$266.11	$266.10	$266.10
Purchase #5	$118.62	7.185%	$127.1428	$127.14	$127.15	$127.10
Purchase #6	$105.40	11.855%	$117.8952	$117.90	$117.90	$117.90
Purchase #7	$116.65	13.141%	$131.979	$131.98	$132.00	$132.00
7 purchase totals =	$869.55		$949.4487	$949.46	$949.50	$949.40