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	$76.77	9.645%	$84.1745	$84.17	$84.15	$84.20
Purchase #2	$217.31	7.651%	$233.9364	$233.94	$233.95	$233.90
Purchase #3	$173.89	13.128%	$196.7183	$196.72	$196.70	$196.70
Purchase #4	$39.75	4.471%	$41.5272	$41.53	$41.55	$41.50
Purchase #5	$132.76	6.823%	$141.8182	$141.82	$141.80	$141.80
Purchase #6	$214.38	11.860%	$239.8055	$239.81	$239.80	$239.80
Purchase #7	$150.82	11.470%	$168.1191	$168.12	$168.10	$168.10
7 purchase totals =	$1,005.68		$1,106.0992	$1,106.11	$1,106.05	$1,106.00