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	$89.37	8.353%	$96.8351	$96.84	$96.85	$96.80
Purchase #2	$245.55	12.180%	$275.458	$275.46	$275.45	$275.50
Purchase #3	$54.74	11.501%	$61.0356	$61.04	$61.05	$61.00
Purchase #4	$87.92	10.260%	$96.9406	$96.94	$96.95	$96.90
Purchase #5	$17.76	4.404%	$18.5422	$18.54	$18.55	$18.50
Purchase #6	$121.55	9.372%	$132.9417	$132.94	$132.95	$132.90
Purchase #7	$87.36	4.342%	$91.1532	$91.15	$91.15	$91.20
7 purchase totals =	$704.25		$772.9064	$772.91	$772.95	$772.80