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	$113.89	3.191%	$117.5242	$117.52	$117.50	$117.50
Purchase #2	$89.78	7.416%	$96.4381	$96.44	$96.45	$96.40
Purchase #3	$169.27	9.205%	$184.8513	$184.85	$184.85	$184.90
Purchase #4	$88.75	13.297%	$100.5511	$100.55	$100.55	$100.60
Purchase #5	$216.74	3.165%	$223.5998	$223.60	$223.60	$223.60
Purchase #6	$39.43	12.551%	$44.3789	$44.38	$44.40	$44.40
Purchase #7	$97.60	13.526%	$110.8014	$110.80	$110.80	$110.80
7 purchase totals =	$815.46		$878.1448	$878.14	$878.15	$878.20