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	$51.31	7.439%	$55.127	$55.13	$55.15	$55.10
Purchase #2	$230.51	10.648%	$255.0547	$255.05	$255.05	$255.10
Purchase #3	$30.46	8.811%	$33.1438	$33.14	$33.15	$33.10
Purchase #4	$26.74	3.316%	$27.6267	$27.63	$27.65	$27.60
Purchase #5	$33.36	6.772%	$35.6191	$35.62	$35.60	$35.60
Purchase #6	$44.87	4.428%	$46.8568	$46.86	$46.85	$46.90
Purchase #7	$48.42	12.197%	$54.3258	$54.33	$54.35	$54.30
7 purchase totals =	$465.67		$507.7539	$507.76	$507.80	$507.70