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	$173.33	10.489%	$191.5106	$191.51	$191.50	$191.50
Purchase #2	$214.65	6.557%	$228.7246	$228.72	$228.70	$228.70
Purchase #3	$91.75	8.748%	$99.7763	$99.78	$99.80	$99.80
Purchase #4	$84.37	4.270%	$87.9726	$87.97	$87.95	$88.00
Purchase #5	$37.92	5.173%	$39.8816	$39.88	$39.90	$39.90
Purchase #6	$84.27	7.156%	$90.3004	$90.30	$90.30	$90.30
Purchase #7	$176.45	13.754%	$200.7189	$200.72	$200.70	$200.70
7 purchase totals =	$862.74		$938.8850	$938.88	$938.85	$938.90