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	$168.95	7.310%	$181.3002	$181.30	$181.30	$181.30
Purchase #2	$101.28	3.743%	$105.0709	$105.07	$105.05	$105.10
Purchase #3	$42.77	12.275%	$48.02	$48.02	$48.00	$48.00
Purchase #4	$185.93	6.864%	$198.6922	$198.69	$198.70	$198.70
Purchase #5	$83.65	6.773%	$89.3156	$89.32	$89.30	$89.30
Purchase #6	$30.68	8.664%	$33.3381	$33.34	$33.35	$33.30
Purchase #7	$120.52	3.139%	$124.3031	$124.30	$124.30	$124.30
7 purchase totals =	$733.78		$780.0401	$780.04	$780.00	$780.00