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	$58.75	5.251%	$61.835	$61.84	$61.85	$61.80
Purchase #2	$139.35	13.613%	$158.3197	$158.32	$158.30	$158.30
Purchase #3	$112.80	6.306%	$119.9132	$119.91	$119.90	$119.90
Purchase #4	$250.83	5.304%	$264.134	$264.13	$264.15	$264.10
Purchase #5	$28.28	12.526%	$31.8224	$31.82	$31.80	$31.80
Purchase #6	$223.81	6.449%	$238.2435	$238.24	$238.25	$238.20
Purchase #7	$87.85	9.694%	$96.3662	$96.37	$96.35	$96.40
7 purchase totals =	$901.67		$970.6340	$970.63	$970.60	$970.50