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	$28.57	12.771%	$32.2187	$32.22	$32.20	$32.20
Purchase #2	$128.95	10.396%	$142.3556	$142.36	$142.35	$142.40
Purchase #3	$136.73	4.323%	$142.6408	$142.64	$142.65	$142.60
Purchase #4	$10.82	11.758%	$12.0922	$12.09	$12.10	$12.10
Purchase #5	$110.69	11.512%	$123.4326	$123.43	$123.45	$123.40
Purchase #6	$91.48	7.260%	$98.1214	$98.12	$98.10	$98.10
Purchase #7	$159.28	12.482%	$179.1613	$179.16	$179.15	$179.20
7 purchase totals =	$666.52		$730.0226	$730.02	$730.00	$730.00