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	$19.90	13.133%	$22.5135	$22.51	$22.50	$22.50
Purchase #2	$184.55	3.121%	$190.3098	$190.31	$190.30	$190.30
Purchase #3	$52.36	7.501%	$56.2875	$56.29	$56.30	$56.30
Purchase #4	$26.52	10.294%	$29.25	$29.25	$29.25	$29.30
Purchase #5	$109.94	13.279%	$124.5389	$124.54	$124.55	$124.50
Purchase #6	$14.96	4.718%	$15.6658	$15.67	$15.65	$15.70
Purchase #7	$161.99	12.282%	$181.8856	$181.89	$181.90	$181.90
7 purchase totals =	$570.22		$620.4511	$620.46	$620.45	$620.50