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	$73.82	3.389%	$76.3218	$76.32	$76.30	$76.30
Purchase #2	$217.73	10.156%	$239.8427	$239.84	$239.85	$239.80
Purchase #3	$241.68	9.485%	$264.6033	$264.60	$264.60	$264.60
Purchase #4	$10.90	13.607%	$12.3832	$12.38	$12.40	$12.40
Purchase #5	$116.54	7.764%	$125.5882	$125.59	$125.60	$125.60
Purchase #6	$101.98	9.787%	$111.9608	$111.96	$111.95	$112.00
Purchase #7	$32.42	4.563%	$33.8993	$33.90	$33.90	$33.90
7 purchase totals =	$795.07		$864.5993	$864.59	$864.60	$864.60