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	$81.52	11.468%	$90.8687	$90.87	$90.85	$90.90
Purchase #2	$182.77	13.726%	$207.857	$207.86	$207.85	$207.90
Purchase #3	$40.79	10.377%	$45.0228	$45.02	$45.00	$45.00
Purchase #4	$110.62	11.212%	$123.0227	$123.02	$123.00	$123.00
Purchase #5	$110.69	8.787%	$120.4163	$120.42	$120.40	$120.40
Purchase #6	$105.56	10.718%	$116.8739	$116.87	$116.85	$116.90
Purchase #7	$212.36	11.428%	$236.6285	$236.63	$236.65	$236.60
7 purchase totals =	$844.31		$940.6899	$940.69	$940.60	$940.70