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	$95.90	7.213%	$102.8173	$102.82	$102.80	$102.80
Purchase #2	$36.42	9.502%	$39.8806	$39.88	$39.90	$39.90
Purchase #3	$17.76	13.366%	$20.1338	$20.13	$20.15	$20.10
Purchase #4	$105.52	13.128%	$119.3727	$119.37	$119.35	$119.40
Purchase #5	$183.47	8.717%	$199.4631	$199.46	$199.45	$199.50
Purchase #6	$95.37	9.380%	$104.3157	$104.32	$104.30	$104.30
Purchase #7	$223.98	4.793%	$234.7154	$234.72	$234.70	$234.70
7 purchase totals =	$758.42		$820.6986	$820.70	$820.65	$820.70