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	$64.75	12.129%	$72.6035	$72.60	$72.60	$72.60
Purchase #2	$99.78	12.678%	$112.4301	$112.43	$112.45	$112.40
Purchase #3	$105.90	3.333%	$109.4296	$109.43	$109.45	$109.40
Purchase #4	$64.35	13.632%	$73.1222	$73.12	$73.10	$73.10
Purchase #5	$60.64	13.531%	$68.8452	$68.85	$68.85	$68.80
Purchase #6	$118.51	9.803%	$130.1275	$130.13	$130.15	$130.10
Purchase #7	$73.36	3.599%	$76.0002	$76.00	$76.00	$76.00
7 purchase totals =	$587.29		$642.5583	$642.56	$642.60	$642.40