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	$226.36	7.670%	$243.7218	$243.72	$243.70	$243.70
Purchase #2	$144.30	4.813%	$151.2452	$151.25	$151.25	$151.20
Purchase #3	$147.91	13.808%	$168.3334	$168.33	$168.35	$168.30
Purchase #4	$214.96	3.764%	$223.0511	$223.05	$223.05	$223.10
Purchase #5	$250.52	11.424%	$279.1394	$279.14	$279.15	$279.10
Purchase #6	$159.93	5.624%	$168.9245	$168.92	$168.90	$168.90
Purchase #7	$6.36	10.673%	$7.0388	$7.04	$7.05	$7.00
7 purchase totals =	$1,150.34		$1,241.4542	$1,241.45	$1,241.45	$1,241.30