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	$64.71	10.145%	$71.2748	$71.27	$71.25	$71.30
Purchase #2	$53.37	11.708%	$59.6186	$59.62	$59.60	$59.60
Purchase #3	$8.40	12.553%	$9.4545	$9.45	$9.45	$9.50
Purchase #4	$75.79	11.369%	$84.4066	$84.41	$84.40	$84.40
Purchase #5	$83.59	7.647%	$89.9821	$89.98	$90.00	$90.00
Purchase #6	$121.35	13.553%	$137.7966	$137.80	$137.80	$137.80
Purchase #7	$55.50	9.193%	$60.6021	$60.60	$60.60	$60.60
7 purchase totals =	$462.71		$513.1353	$513.13	$513.10	$513.20