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	$31.59	3.580%	$32.7209	$32.72	$32.70	$32.70
Purchase #2	$176.82	5.502%	$186.5486	$186.55	$186.55	$186.50
Purchase #3	$158.71	6.106%	$168.4008	$168.40	$168.40	$168.40
Purchase #4	$49.65	3.219%	$51.2482	$51.25	$51.25	$51.20
Purchase #5	$210.56	6.216%	$223.6484	$223.65	$223.65	$223.60
Purchase #6	$91.52	13.776%	$104.1278	$104.13	$104.15	$104.10
Purchase #7	$31.52	5.402%	$33.2227	$33.22	$33.20	$33.20
7 purchase totals =	$750.37		$799.9174	$799.92	$799.90	$799.70