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	$130.44	10.510%	$144.1492	$144.15	$144.15	$144.10
Purchase #2	$106.88	4.102%	$111.2642	$111.26	$111.25	$111.30
Purchase #3	$146.35	8.421%	$158.6741	$158.67	$158.65	$158.70
Purchase #4	$72.35	8.585%	$78.5612	$78.56	$78.55	$78.60
Purchase #5	$83.30	3.129%	$85.9065	$85.91	$85.90	$85.90
Purchase #6	$244.53	9.110%	$266.8067	$266.81	$266.80	$266.80
Purchase #7	$64.70	3.437%	$66.9237	$66.92	$66.90	$66.90
7 purchase totals =	$848.55		$912.2856	$912.28	$912.20	$912.30