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	$137.77	8.162%	$149.0148	$149.01	$149.00	$149.00
Purchase #2	$16.91	11.260%	$18.8141	$18.81	$18.80	$18.80
Purchase #3	$32.63	13.532%	$37.0455	$37.05	$37.05	$37.00
Purchase #4	$90.82	11.115%	$100.9146	$100.91	$100.90	$100.90
Purchase #5	$156.89	5.251%	$165.1283	$165.13	$165.15	$165.10
Purchase #6	$47.86	12.152%	$53.6759	$53.68	$53.70	$53.70
Purchase #7	$86.25	5.861%	$91.3051	$91.31	$91.30	$91.30
7 purchase totals =	$569.13		$615.8983	$615.90	$615.90	$615.80