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	$198.27	12.439%	$222.9328	$222.93	$222.95	$222.90
Purchase #2	$77.81	6.846%	$83.1369	$83.14	$83.15	$83.10
Purchase #3	$139.30	10.747%	$154.2706	$154.27	$154.25	$154.30
Purchase #4	$120.65	5.580%	$127.3823	$127.38	$127.40	$127.40
Purchase #5	$118.63	8.144%	$128.2912	$128.29	$128.30	$128.30
Purchase #6	$44.94	9.736%	$49.3154	$49.32	$49.30	$49.30
Purchase #7	$102.69	12.321%	$115.3424	$115.34	$115.35	$115.30
7 purchase totals =	$802.29		$880.6716	$880.67	$880.70	$880.60