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	$135.68	3.574%	$140.5292	$140.53	$140.55	$140.50
Purchase #2	$84.72	5.826%	$89.6558	$89.66	$89.65	$89.70
Purchase #3	$166.94	11.149%	$185.5521	$185.55	$185.55	$185.60
Purchase #4	$61.87	5.578%	$65.3211	$65.32	$65.30	$65.30
Purchase #5	$129.63	10.528%	$143.2774	$143.28	$143.30	$143.30
Purchase #6	$227.48	9.793%	$249.7571	$249.76	$249.75	$249.80
Purchase #7	$17.93	11.730%	$20.0332	$20.03	$20.05	$20.00
7 purchase totals =	$824.25		$894.1259	$894.13	$894.15	$894.20