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	$29.34	10.657%	$32.4668	$32.47	$32.45	$32.50
Purchase #2	$105.61	5.172%	$111.0721	$111.07	$111.05	$111.10
Purchase #3	$93.62	8.377%	$101.4625	$101.46	$101.45	$101.50
Purchase #4	$229.34	7.193%	$245.8364	$245.84	$245.85	$245.80
Purchase #5	$181.53	9.859%	$199.427	$199.43	$199.45	$199.40
Purchase #6	$19.89	10.405%	$21.9596	$21.96	$21.95	$22.00
Purchase #7	$160.67	4.627%	$168.1042	$168.10	$168.10	$168.10
7 purchase totals =	$820.00		$880.3286	$880.33	$880.30	$880.40