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	$215.99	12.140%	$242.2112	$242.21	$242.20	$242.20
Purchase #2	$190.32	6.760%	$203.1856	$203.19	$203.20	$203.20
Purchase #3	$196.96	13.487%	$223.524	$223.52	$223.50	$223.50
Purchase #4	$96.89	11.224%	$107.7649	$107.76	$107.75	$107.80
Purchase #5	$29.54	9.833%	$32.4447	$32.44	$32.45	$32.40
Purchase #6	$115.88	10.162%	$127.6557	$127.66	$127.65	$127.70
Purchase #7	$80.60	12.215%	$90.4453	$90.45	$90.45	$90.40
7 purchase totals =	$926.18		$1,027.2314	$1,027.23	$1,027.20	$1,027.20