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	$145.63	7.333%	$156.309	$156.31	$156.30	$156.30
Purchase #2	$158.98	4.380%	$165.9433	$165.94	$165.95	$165.90
Purchase #3	$226.83	10.810%	$251.3503	$251.35	$251.35	$251.40
Purchase #4	$131.53	12.446%	$147.9002	$147.90	$147.90	$147.90
Purchase #5	$20.33	13.842%	$23.1441	$23.14	$23.15	$23.10
Purchase #6	$229.56	11.652%	$256.3083	$256.31	$256.30	$256.30
Purchase #7	$133.82	6.660%	$142.7324	$142.73	$142.75	$142.70
7 purchase totals =	$1,046.68		$1,143.6876	$1,143.68	$1,143.70	$1,143.60