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	$64.28	5.446%	$67.7807	$67.78	$67.80	$67.80
Purchase #2	$241.90	3.550%	$250.4875	$250.49	$250.50	$250.50
Purchase #3	$128.83	8.785%	$140.1477	$140.15	$140.15	$140.10
Purchase #4	$230.33	11.722%	$257.3293	$257.33	$257.35	$257.30
Purchase #5	$129.77	11.259%	$144.3808	$144.38	$144.40	$144.40
Purchase #6	$58.27	7.707%	$62.7609	$62.76	$62.75	$62.80
Purchase #7	$37.28	13.157%	$42.1849	$42.18	$42.20	$42.20
7 purchase totals =	$890.66		$965.0718	$965.07	$965.15	$965.10