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	$85.89	5.223%	$90.376	$90.38	$90.40	$90.40
Purchase #2	$135.84	3.769%	$140.9598	$140.96	$140.95	$141.00
Purchase #3	$117.32	10.434%	$129.5612	$129.56	$129.55	$129.60
Purchase #4	$164.78	4.554%	$172.2841	$172.28	$172.30	$172.30
Purchase #5	$40.79	11.425%	$45.4503	$45.45	$45.45	$45.50
Purchase #6	$160.92	9.207%	$175.7359	$175.74	$175.75	$175.70
Purchase #7	$166.37	5.556%	$175.6135	$175.61	$175.60	$175.60
7 purchase totals =	$871.91		$929.9808	$929.98	$930.00	$930.10