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	$14.54	7.155%	$15.5803	$15.58	$15.60	$15.60
Purchase #2	$64.92	4.188%	$67.6388	$67.64	$67.65	$67.60
Purchase #3	$224.51	11.679%	$250.7305	$250.73	$250.75	$250.70
Purchase #4	$167.55	10.343%	$184.8797	$184.88	$184.90	$184.90
Purchase #5	$91.73	9.121%	$100.0967	$100.10	$100.10	$100.10
Purchase #6	$77.65	10.525%	$85.8227	$85.82	$85.80	$85.80
Purchase #7	$244.49	4.749%	$256.1008	$256.10	$256.10	$256.10
7 purchase totals =	$885.39		$960.8495	$960.85	$960.90	$960.80