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	$208.85	8.379%	$226.3495	$226.35	$226.35	$226.30
Purchase #2	$148.88	12.221%	$167.0746	$167.07	$167.05	$167.10
Purchase #3	$176.59	8.379%	$191.3865	$191.39	$191.40	$191.40
Purchase #4	$151.58	11.187%	$168.5373	$168.54	$168.55	$168.50
Purchase #5	$106.52	4.331%	$111.1334	$111.13	$111.15	$111.10
Purchase #6	$17.66	6.684%	$18.8404	$18.84	$18.85	$18.80
Purchase #7	$45.38	8.436%	$49.2083	$49.21	$49.20	$49.20
7 purchase totals =	$855.46		$932.5300	$932.53	$932.55	$932.40