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	$29.83	12.664%	$33.6077	$33.61	$33.60	$33.60
Purchase #2	$152.56	4.118%	$158.8424	$158.84	$158.85	$158.80
Purchase #3	$92.32	6.378%	$98.2082	$98.21	$98.20	$98.20
Purchase #4	$99.75	4.780%	$104.5181	$104.52	$104.50	$104.50
Purchase #5	$87.83	5.477%	$92.6404	$92.64	$92.65	$92.60
Purchase #6	$243.70	11.449%	$271.6012	$271.60	$271.60	$271.60
Purchase #7	$32.60	3.687%	$33.802	$33.80	$33.80	$33.80
7 purchase totals =	$738.59		$793.2200	$793.22	$793.20	$793.10