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	$203.52	13.174%	$230.3317	$230.33	$230.35	$230.30
Purchase #2	$112.32	12.640%	$126.5172	$126.52	$126.50	$126.50
Purchase #3	$66.95	7.702%	$72.1065	$72.11	$72.10	$72.10
Purchase #4	$42.28	6.599%	$45.0701	$45.07	$45.05	$45.10
Purchase #5	$84.32	7.114%	$90.3185	$90.32	$90.30	$90.30
Purchase #6	$166.93	10.183%	$183.9285	$183.93	$183.95	$183.90
Purchase #7	$89.78	10.524%	$99.2284	$99.23	$99.25	$99.20
7 purchase totals =	$766.10		$847.5009	$847.51	$847.50	$847.40