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	$237.53	3.870%	$246.7224	$246.72	$246.70	$246.70
Purchase #2	$151.79	13.596%	$172.4274	$172.43	$172.45	$172.40
Purchase #3	$30.82	9.728%	$33.8182	$33.82	$33.80	$33.80
Purchase #4	$88.53	9.468%	$96.912	$96.91	$96.90	$96.90
Purchase #5	$176.28	10.710%	$195.1596	$195.16	$195.15	$195.20
Purchase #6	$79.32	13.107%	$89.7165	$89.72	$89.70	$89.70
Purchase #7	$15.89	10.479%	$17.5551	$17.56	$17.55	$17.60
7 purchase totals =	$780.16		$852.3112	$852.32	$852.25	$852.30