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	$167.43	12.384%	$188.1645	$188.16	$188.15	$188.20
Purchase #2	$27.26	8.303%	$29.5234	$29.52	$29.50	$29.50
Purchase #3	$127.32	12.204%	$142.8581	$142.86	$142.85	$142.90
Purchase #4	$198.46	12.836%	$223.9343	$223.93	$223.95	$223.90
Purchase #5	$19.70	9.493%	$21.5701	$21.57	$21.55	$21.60
Purchase #6	$241.68	12.275%	$271.3462	$271.35	$271.35	$271.30
Purchase #7	$39.96	13.419%	$45.3222	$45.32	$45.30	$45.30
7 purchase totals =	$821.81		$922.7188	$922.71	$922.65	$922.70