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	$85.44	4.737%	$89.4873	$89.49	$89.50	$89.50
Purchase #2	$80.60	10.424%	$89.0017	$89.00	$89.00	$89.00
Purchase #3	$85.83	12.352%	$96.4317	$96.43	$96.45	$96.40
Purchase #4	$83.40	7.461%	$89.6225	$89.62	$89.60	$89.60
Purchase #5	$73.26	6.401%	$77.9494	$77.95	$77.95	$77.90
Purchase #6	$230.46	7.678%	$248.1547	$248.15	$248.15	$248.20
Purchase #7	$126.83	12.756%	$143.0084	$143.01	$143.00	$143.00
7 purchase totals =	$765.82		$833.6557	$833.65	$833.65	$833.60