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	$84.83	6.851%	$90.6417	$90.64	$90.65	$90.60
Purchase #2	$158.40	12.483%	$178.1731	$178.17	$178.15	$178.20
Purchase #3	$211.74	12.306%	$237.7967	$237.80	$237.80	$237.80
Purchase #4	$193.26	9.404%	$211.4342	$211.43	$211.45	$211.40
Purchase #5	$166.59	13.142%	$188.4833	$188.48	$188.50	$188.50
Purchase #6	$89.46	12.792%	$100.9037	$100.90	$100.90	$100.90
Purchase #7	$249.71	4.830%	$261.771	$261.77	$261.75	$261.80
7 purchase totals =	$1,153.99		$1,269.2037	$1,269.19	$1,269.20	$1,269.20