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	$105.31	3.548%	$109.0464	$109.05	$109.05	$109.00
Purchase #2	$60.93	3.834%	$63.2661	$63.27	$63.25	$63.30
Purchase #3	$235.91	3.800%	$244.8746	$244.87	$244.85	$244.90
Purchase #4	$50.55	6.104%	$53.6356	$53.64	$53.65	$53.60
Purchase #5	$236.29	13.684%	$268.6239	$268.62	$268.60	$268.60
Purchase #6	$212.70	5.136%	$223.6243	$223.62	$223.60	$223.60
Purchase #7	$123.52	3.459%	$127.7926	$127.79	$127.80	$127.80
7 purchase totals =	$1,025.21		$1,090.8635	$1,090.86	$1,090.80	$1,090.80