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	$184.33	10.201%	$203.1335	$203.13	$203.15	$203.10
Purchase #2	$249.43	8.859%	$271.527	$271.53	$271.55	$271.50
Purchase #3	$237.76	7.268%	$255.0404	$255.04	$255.05	$255.00
Purchase #4	$124.31	7.525%	$133.6643	$133.66	$133.65	$133.70
Purchase #5	$149.46	12.454%	$168.0737	$168.07	$168.05	$168.10
Purchase #6	$18.61	9.762%	$20.4267	$20.43	$20.45	$20.40
Purchase #7	$105.37	5.366%	$111.0242	$111.02	$111.00	$111.00
7 purchase totals =	$1,069.27		$1,162.8898	$1,162.88	$1,162.90	$1,162.80