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	$29.52	6.869%	$31.5477	$31.55	$31.55	$31.50
Purchase #2	$155.90	6.499%	$166.0319	$166.03	$166.05	$166.00
Purchase #3	$228.98	11.576%	$255.4867	$255.49	$255.50	$255.50
Purchase #4	$232.84	3.851%	$241.8067	$241.81	$241.80	$241.80
Purchase #5	$28.81	12.122%	$32.3023	$32.30	$32.30	$32.30
Purchase #6	$40.39	13.558%	$45.8661	$45.87	$45.85	$45.90
Purchase #7	$18.87	10.578%	$20.8661	$20.87	$20.85	$20.90
7 purchase totals =	$735.31		$793.9075	$793.92	$793.90	$793.90