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	$88.99	12.494%	$100.1084	$100.11	$100.10	$100.10
Purchase #2	$248.39	8.206%	$268.7729	$268.77	$268.75	$268.80
Purchase #3	$137.43	7.266%	$147.4157	$147.42	$147.40	$147.40
Purchase #4	$56.60	13.545%	$64.2665	$64.27	$64.25	$64.30
Purchase #5	$250.95	9.339%	$274.3862	$274.39	$274.40	$274.40
Purchase #6	$62.79	13.844%	$71.4826	$71.48	$71.50	$71.50
Purchase #7	$242.60	5.700%	$256.4282	$256.43	$256.45	$256.40
7 purchase totals =	$1,087.75		$1,182.8605	$1,182.87	$1,182.85	$1,182.90