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	$161.56	5.378%	$170.2487	$170.25	$170.25	$170.20
Purchase #2	$9.79	3.625%	$10.1449	$10.14	$10.15	$10.10
Purchase #3	$123.49	6.598%	$131.6379	$131.64	$131.65	$131.60
Purchase #4	$47.69	6.702%	$50.8862	$50.89	$50.90	$50.90
Purchase #5	$100.99	11.122%	$112.2221	$112.22	$112.20	$112.20
Purchase #6	$73.61	11.301%	$81.9287	$81.93	$81.95	$81.90
Purchase #7	$41.59	4.188%	$43.3318	$43.33	$43.35	$43.30
7 purchase totals =	$558.72		$600.4003	$600.40	$600.45	$600.20