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	$47.48	12.410%	$53.3723	$53.37	$53.35	$53.40
Purchase #2	$159.27	12.635%	$179.3938	$179.39	$179.40	$179.40
Purchase #3	$229.36	11.316%	$255.3144	$255.31	$255.30	$255.30
Purchase #4	$103.74	9.518%	$113.614	$113.61	$113.60	$113.60
Purchase #5	$213.97	11.441%	$238.4503	$238.45	$238.45	$238.50
Purchase #6	$53.71	4.599%	$56.1801	$56.18	$56.20	$56.20
Purchase #7	$49.37	11.687%	$55.1399	$55.14	$55.15	$55.10
7 purchase totals =	$856.90		$951.4648	$951.45	$951.45	$951.50