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	$166.60	3.261%	$172.0328	$172.03	$172.05	$172.00
Purchase #2	$12.77	6.357%	$13.5818	$13.58	$13.60	$13.60
Purchase #3	$86.30	4.606%	$90.275	$90.28	$90.30	$90.30
Purchase #4	$223.73	5.654%	$236.3797	$236.38	$236.40	$236.40
Purchase #5	$101.37	11.572%	$113.1005	$113.10	$113.10	$113.10
Purchase #6	$64.97	13.410%	$73.6825	$73.68	$73.70	$73.70
Purchase #7	$124.55	13.314%	$141.1326	$141.13	$141.15	$141.10
7 purchase totals =	$780.29		$840.1849	$840.18	$840.30	$840.20