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	$141.54	12.114%	$158.6862	$158.69	$158.70	$158.70
Purchase #2	$91.42	12.720%	$103.0486	$103.05	$103.05	$103.00
Purchase #3	$45.83	3.700%	$47.5257	$47.53	$47.55	$47.50
Purchase #4	$160.42	3.631%	$166.2449	$166.24	$166.25	$166.20
Purchase #5	$24.44	3.644%	$25.3306	$25.33	$25.35	$25.30
Purchase #6	$217.40	11.727%	$242.8945	$242.89	$242.90	$242.90
Purchase #7	$56.95	3.673%	$59.0418	$59.04	$59.05	$59.00
7 purchase totals =	$738.00		$802.7723	$802.77	$802.85	$802.60