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	$97.43	3.194%	$100.5419	$100.54	$100.55	$100.50
Purchase #2	$155.92	10.545%	$172.3618	$172.36	$172.35	$172.40
Purchase #3	$55.60	6.503%	$59.2157	$59.22	$59.20	$59.20
Purchase #4	$79.70	3.868%	$82.7828	$82.78	$82.80	$82.80
Purchase #5	$127.89	3.109%	$131.8661	$131.87	$131.85	$131.90
Purchase #6	$38.89	9.148%	$42.4477	$42.45	$42.45	$42.40
Purchase #7	$16.89	10.417%	$18.6494	$18.65	$18.65	$18.60
7 purchase totals =	$572.32		$607.8654	$607.87	$607.85	$607.80