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	$76.61	8.729%	$83.2973	$83.30	$83.30	$83.30
Purchase #2	$49.72	8.487%	$53.9397	$53.94	$53.95	$53.90
Purchase #3	$232.90	6.551%	$248.1573	$248.16	$248.15	$248.20
Purchase #4	$63.31	6.794%	$67.6113	$67.61	$67.60	$67.60
Purchase #5	$20.43	6.543%	$21.7667	$21.77	$21.75	$21.80
Purchase #6	$46.59	4.715%	$48.7867	$48.79	$48.80	$48.80
Purchase #7	$130.64	9.655%	$143.2533	$143.25	$143.25	$143.30
7 purchase totals =	$620.20		$666.8123	$666.82	$666.80	$666.90