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	$123.45	10.826%	$136.8147	$136.81	$136.80	$136.80
Purchase #2	$35.64	4.341%	$37.1871	$37.19	$37.20	$37.20
Purchase #3	$196.37	5.697%	$207.5572	$207.56	$207.55	$207.60
Purchase #4	$130.71	13.184%	$147.9428	$147.94	$147.95	$147.90
Purchase #5	$48.26	10.154%	$53.1603	$53.16	$53.15	$53.20
Purchase #6	$243.80	11.614%	$272.1149	$272.11	$272.10	$272.10
Purchase #7	$90.67	11.242%	$100.8631	$100.86	$100.85	$100.90
7 purchase totals =	$868.90		$955.6401	$955.63	$955.60	$955.70