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	$30.51	8.618%	$33.1394	$33.14	$33.15	$33.10
Purchase #2	$149.40	6.698%	$159.4068	$159.41	$159.40	$159.40
Purchase #3	$161.83	11.481%	$180.4097	$180.41	$180.40	$180.40
Purchase #4	$182.57	7.624%	$196.4891	$196.49	$196.50	$196.50
Purchase #5	$219.99	7.509%	$236.509	$236.51	$236.50	$236.50
Purchase #6	$51.82	4.854%	$54.3353	$54.34	$54.35	$54.30
Purchase #7	$84.30	8.384%	$91.3677	$91.37	$91.35	$91.40
7 purchase totals =	$880.42		$951.6570	$951.67	$951.65	$951.60