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	$136.75	5.771%	$144.6418	$144.64	$144.65	$144.60
Purchase #2	$182.36	9.831%	$200.2878	$200.29	$200.30	$200.30
Purchase #3	$57.49	13.675%	$65.3518	$65.35	$65.35	$65.40
Purchase #4	$67.96	8.297%	$73.5986	$73.60	$73.60	$73.60
Purchase #5	$92.85	11.259%	$103.304	$103.30	$103.30	$103.30
Purchase #6	$80.99	10.261%	$89.3004	$89.30	$89.30	$89.30
Purchase #7	$26.65	11.220%	$29.6401	$29.64	$29.65	$29.60
7 purchase totals =	$645.05		$706.1245	$706.12	$706.15	$706.10