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	$82.73	8.457%	$89.7265	$89.73	$89.75	$89.70
Purchase #2	$69.32	6.695%	$73.961	$73.96	$73.95	$74.00
Purchase #3	$191.96	12.806%	$216.5424	$216.54	$216.55	$216.50
Purchase #4	$202.67	12.703%	$228.4152	$228.42	$228.40	$228.40
Purchase #5	$79.62	4.600%	$83.2825	$83.28	$83.30	$83.30
Purchase #6	$48.77	3.559%	$50.5057	$50.51	$50.50	$50.50
Purchase #7	$87.26	3.290%	$90.1309	$90.13	$90.15	$90.10
7 purchase totals =	$762.33		$832.5642	$832.57	$832.60	$832.50