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	$77.70	8.550%	$84.3434	$84.34	$84.35	$84.30
Purchase #2	$122.67	11.362%	$136.6078	$136.61	$136.60	$136.60
Purchase #3	$175.91	5.338%	$185.3001	$185.30	$185.30	$185.30
Purchase #4	$218.36	6.763%	$233.1277	$233.13	$233.15	$233.10
Purchase #5	$246.65	11.830%	$275.8287	$275.83	$275.85	$275.80
Purchase #6	$90.44	10.111%	$99.5844	$99.58	$99.60	$99.60
Purchase #7	$116.60	13.727%	$132.6057	$132.61	$132.60	$132.60
7 purchase totals =	$1,048.33		$1,147.3978	$1,147.40	$1,147.45	$1,147.30