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	$147.75	11.834%	$165.2347	$165.23	$165.25	$165.20
Purchase #2	$44.36	4.399%	$46.3114	$46.31	$46.30	$46.30
Purchase #3	$142.65	12.364%	$160.2872	$160.29	$160.30	$160.30
Purchase #4	$180.42	3.276%	$186.3306	$186.33	$186.35	$186.30
Purchase #5	$40.56	5.334%	$42.7235	$42.72	$42.70	$42.70
Purchase #6	$26.56	4.229%	$27.6832	$27.68	$27.70	$27.70
Purchase #7	$9.51	10.818%	$10.5388	$10.54	$10.55	$10.50
7 purchase totals =	$591.81		$639.1094	$639.10	$639.15	$639.00