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	$140.86	6.132%	$149.4975	$149.50	$149.50	$149.50
Purchase #2	$229.61	10.613%	$253.9785	$253.98	$254.00	$254.00
Purchase #3	$154.26	9.770%	$169.3312	$169.33	$169.35	$169.30
Purchase #4	$53.52	11.702%	$59.7829	$59.78	$59.80	$59.80
Purchase #5	$113.30	12.697%	$127.6857	$127.69	$127.70	$127.70
Purchase #6	$81.35	8.788%	$88.499	$88.50	$88.50	$88.50
Purchase #7	$231.59	12.117%	$259.6518	$259.65	$259.65	$259.70
7 purchase totals =	$1,004.49		$1,108.4266	$1,108.43	$1,108.50	$1,108.50