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	$154.39	12.199%	$173.224	$173.22	$173.20	$173.20
Purchase #2	$126.75	3.463%	$131.1394	$131.14	$131.15	$131.10
Purchase #3	$93.55	13.865%	$106.5207	$106.52	$106.50	$106.50
Purchase #4	$68.62	4.466%	$71.6846	$71.68	$71.70	$71.70
Purchase #5	$135.25	12.589%	$152.2766	$152.28	$152.30	$152.30
Purchase #6	$73.68	13.524%	$83.6445	$83.64	$83.65	$83.60
Purchase #7	$246.63	5.316%	$259.7409	$259.74	$259.75	$259.70
7 purchase totals =	$898.87		$978.2307	$978.22	$978.25	$978.10