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	$37.64	12.329%	$42.2806	$42.28	$42.30	$42.30
Purchase #2	$97.97	4.442%	$102.3218	$102.32	$102.30	$102.30
Purchase #3	$194.91	7.418%	$209.3684	$209.37	$209.35	$209.40
Purchase #4	$33.98	13.444%	$38.5483	$38.55	$38.55	$38.50
Purchase #5	$89.90	12.278%	$100.9379	$100.94	$100.95	$100.90
Purchase #6	$144.65	3.201%	$149.2802	$149.28	$149.30	$149.30
Purchase #7	$202.67	10.366%	$223.6788	$223.68	$223.70	$223.70
7 purchase totals =	$801.72		$866.4160	$866.42	$866.45	$866.40