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	$63.90	13.268%	$72.3783	$72.38	$72.40	$72.40
Purchase #2	$114.39	11.535%	$127.5849	$127.58	$127.60	$127.60
Purchase #3	$97.26	4.254%	$101.3974	$101.40	$101.40	$101.40
Purchase #4	$116.66	5.122%	$122.6353	$122.64	$122.65	$122.60
Purchase #5	$19.33	12.675%	$21.7801	$21.78	$21.80	$21.80
Purchase #6	$18.45	3.148%	$19.0308	$19.03	$19.05	$19.00
Purchase #7	$82.58	11.107%	$91.7522	$91.75	$91.75	$91.80
7 purchase totals =	$512.57		$556.5590	$556.56	$556.65	$556.60