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	$107.78	7.779%	$116.1642	$116.16	$116.15	$116.20
Purchase #2	$89.76	10.783%	$99.4388	$99.44	$99.45	$99.40
Purchase #3	$179.83	6.447%	$191.4236	$191.42	$191.40	$191.40
Purchase #4	$147.69	12.629%	$166.3418	$166.34	$166.35	$166.30
Purchase #5	$232.43	8.104%	$251.2661	$251.27	$251.25	$251.30
Purchase #6	$197.81	5.356%	$208.4047	$208.40	$208.40	$208.40
Purchase #7	$244.80	7.563%	$263.3142	$263.31	$263.30	$263.30
7 purchase totals =	$1,200.10		$1,296.3534	$1,296.34	$1,296.30	$1,296.30