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	$31.47	11.606%	$35.1224	$35.12	$35.10	$35.10
Purchase #2	$230.43	8.687%	$250.4475	$250.45	$250.45	$250.40
Purchase #3	$23.68	13.612%	$26.9033	$26.90	$26.90	$26.90
Purchase #4	$33.45	11.760%	$37.3837	$37.38	$37.40	$37.40
Purchase #5	$248.72	7.787%	$268.0878	$268.09	$268.10	$268.10
Purchase #6	$199.99	13.307%	$226.6027	$226.60	$226.60	$226.60
Purchase #7	$248.48	12.297%	$279.0356	$279.04	$279.05	$279.00
7 purchase totals =	$1,016.22		$1,123.5830	$1,123.58	$1,123.60	$1,123.50