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	$249.85	8.824%	$271.8968	$271.90	$271.90	$271.90
Purchase #2	$165.49	11.467%	$184.4667	$184.47	$184.45	$184.50
Purchase #3	$237.80	10.315%	$262.3291	$262.33	$262.35	$262.30
Purchase #4	$163.42	13.677%	$185.771	$185.77	$185.75	$185.80
Purchase #5	$125.39	4.382%	$130.8846	$130.88	$130.90	$130.90
Purchase #6	$83.31	12.172%	$93.4505	$93.45	$93.45	$93.50
Purchase #7	$216.83	13.222%	$245.4993	$245.50	$245.50	$245.50
7 purchase totals =	$1,242.09		$1,374.2980	$1,374.30	$1,374.30	$1,374.40