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	$220.32	9.476%	$241.1975	$241.20	$241.20	$241.20
Purchase #2	$152.44	8.518%	$165.4248	$165.42	$165.40	$165.40
Purchase #3	$249.48	11.753%	$278.8014	$278.80	$278.80	$278.80
Purchase #4	$153.27	3.661%	$158.8812	$158.88	$158.90	$158.90
Purchase #5	$46.31	13.424%	$52.5267	$52.53	$52.55	$52.50
Purchase #6	$242.46	4.813%	$254.1296	$254.13	$254.15	$254.10
Purchase #7	$92.82	12.834%	$104.7325	$104.73	$104.75	$104.70
7 purchase totals =	$1,157.10		$1,255.6937	$1,255.69	$1,255.75	$1,255.60