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	$135.82	10.361%	$149.8923	$149.89	$149.90	$149.90
Purchase #2	$28.44	4.129%	$29.6143	$29.61	$29.60	$29.60
Purchase #3	$163.87	4.755%	$171.662	$171.66	$171.65	$171.70
Purchase #4	$83.77	9.378%	$91.626	$91.63	$91.65	$91.60
Purchase #5	$113.70	3.700%	$117.9069	$117.91	$117.90	$117.90
Purchase #6	$74.66	12.312%	$83.8521	$83.85	$83.85	$83.90
Purchase #7	$244.52	4.536%	$255.6114	$255.61	$255.60	$255.60
7 purchase totals =	$844.78		$900.1650	$900.16	$900.15	$900.20