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	$240.41	6.198%	$255.3106	$255.31	$255.30	$255.30
Purchase #2	$67.43	10.602%	$74.5789	$74.58	$74.60	$74.60
Purchase #3	$49.43	5.420%	$52.1091	$52.11	$52.10	$52.10
Purchase #4	$75.29	9.288%	$82.2829	$82.28	$82.30	$82.30
Purchase #5	$138.32	12.555%	$155.6861	$155.69	$155.70	$155.70
Purchase #6	$61.34	9.608%	$67.2335	$67.23	$67.25	$67.20
Purchase #7	$250.48	5.549%	$264.3791	$264.38	$264.40	$264.40
7 purchase totals =	$882.70		$951.5802	$951.58	$951.65	$951.60