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	$40.73	9.343%	$44.5354	$44.54	$44.55	$44.50
Purchase #2	$204.52	9.118%	$223.1681	$223.17	$223.15	$223.20
Purchase #3	$153.77	11.555%	$171.5381	$171.54	$171.55	$171.50
Purchase #4	$87.49	12.640%	$98.5487	$98.55	$98.55	$98.50
Purchase #5	$159.61	3.485%	$165.1724	$165.17	$165.15	$165.20
Purchase #6	$12.49	10.854%	$13.8457	$13.85	$13.85	$13.80
Purchase #7	$185.56	6.706%	$198.0037	$198.00	$198.00	$198.00
7 purchase totals =	$844.17		$914.8121	$914.82	$914.80	$914.70