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	$83.35	8.632%	$90.5448	$90.54	$90.55	$90.50
Purchase #2	$40.35	5.110%	$42.4119	$42.41	$42.40	$42.40
Purchase #3	$139.71	8.204%	$151.1718	$151.17	$151.15	$151.20
Purchase #4	$89.62	3.381%	$92.6501	$92.65	$92.65	$92.70
Purchase #5	$67.86	9.583%	$74.363	$74.36	$74.35	$74.40
Purchase #6	$168.26	11.223%	$187.1438	$187.14	$187.15	$187.10
Purchase #7	$190.34	6.673%	$203.0414	$203.04	$203.05	$203.00
7 purchase totals =	$779.49		$841.3268	$841.31	$841.30	$841.30