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	$115.98	10.789%	$128.4931	$128.49	$128.50	$128.50
Purchase #2	$149.50	6.871%	$159.7721	$159.77	$159.75	$159.80
Purchase #3	$127.72	4.620%	$133.6207	$133.62	$133.60	$133.60
Purchase #4	$181.73	10.479%	$200.7735	$200.77	$200.75	$200.80
Purchase #5	$109.94	8.185%	$118.9386	$118.94	$118.95	$118.90
Purchase #6	$85.58	13.542%	$97.1692	$97.17	$97.15	$97.20
Purchase #7	$241.58	8.282%	$261.5877	$261.59	$261.60	$261.60
7 purchase totals =	$1,012.03		$1,100.3549	$1,100.35	$1,100.30	$1,100.40