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	$29.28	13.713%	$33.2952	$33.30	$33.30	$33.30
Purchase #2	$147.38	4.327%	$153.7571	$153.76	$153.75	$153.80
Purchase #3	$37.86	3.132%	$39.0458	$39.05	$39.05	$39.00
Purchase #4	$77.38	7.142%	$82.9065	$82.91	$82.90	$82.90
Purchase #5	$138.45	10.453%	$152.9222	$152.92	$152.90	$152.90
Purchase #6	$72.28	3.778%	$75.0107	$75.01	$75.00	$75.00
Purchase #7	$58.84	6.374%	$62.5905	$62.59	$62.60	$62.60
7 purchase totals =	$561.47		$599.5280	$599.54	$599.50	$599.50