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	$115.80	12.866%	$130.6988	$130.70	$130.70	$130.70
Purchase #2	$228.59	8.566%	$248.171	$248.17	$248.15	$248.20
Purchase #3	$49.43	10.429%	$54.5851	$54.59	$54.60	$54.60
Purchase #4	$143.25	4.853%	$150.2019	$150.20	$150.20	$150.20
Purchase #5	$60.34	7.626%	$64.9415	$64.94	$64.95	$64.90
Purchase #6	$157.29	4.783%	$164.8132	$164.81	$164.80	$164.80
Purchase #7	$174.49	8.259%	$188.9011	$188.90	$188.90	$188.90
7 purchase totals =	$929.19		$1,002.3126	$1,002.31	$1,002.30	$1,002.30