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	$137.85	6.257%	$146.4753	$146.48	$146.50	$146.50
Purchase #2	$174.46	3.705%	$180.9237	$180.92	$180.90	$180.90
Purchase #3	$135.91	11.354%	$151.3412	$151.34	$151.35	$151.30
Purchase #4	$126.73	11.309%	$141.0619	$141.06	$141.05	$141.10
Purchase #5	$50.49	7.111%	$54.0803	$54.08	$54.10	$54.10
Purchase #6	$217.31	10.503%	$240.1341	$240.13	$240.15	$240.10
Purchase #7	$28.52	13.251%	$32.2992	$32.30	$32.30	$32.30
7 purchase totals =	$871.27		$946.3157	$946.31	$946.35	$946.30