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	$27.61	10.732%	$30.5731	$30.57	$30.55	$30.60
Purchase #2	$5.27	10.432%	$5.8198	$5.82	$5.80	$5.80
Purchase #3	$182.56	5.385%	$192.3909	$192.39	$192.40	$192.40
Purchase #4	$178.93	3.526%	$185.2391	$185.24	$185.25	$185.20
Purchase #5	$48.68	13.261%	$55.1355	$55.14	$55.15	$55.10
Purchase #6	$196.28	7.457%	$210.9166	$210.92	$210.90	$210.90
Purchase #7	$99.43	9.166%	$108.5438	$108.54	$108.55	$108.50
7 purchase totals =	$738.76		$788.6188	$788.62	$788.60	$788.50