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	$52.73	6.532%	$56.1743	$56.17	$56.15	$56.20
Purchase #2	$53.73	4.316%	$56.049	$56.05	$56.05	$56.00
Purchase #3	$249.86	4.678%	$261.5485	$261.55	$261.55	$261.50
Purchase #4	$67.76	3.839%	$70.3613	$70.36	$70.35	$70.40
Purchase #5	$120.73	10.370%	$133.2497	$133.25	$133.25	$133.20
Purchase #6	$59.41	3.839%	$61.6907	$61.69	$61.70	$61.70
Purchase #7	$248.37	9.862%	$272.8642	$272.86	$272.85	$272.90
7 purchase totals =	$852.59		$911.9377	$911.93	$911.90	$911.90