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	$104.90	8.521%	$113.8385	$113.84	$113.85	$113.80
Purchase #2	$125.50	4.426%	$131.0546	$131.05	$131.05	$131.10
Purchase #3	$228.86	13.448%	$259.6371	$259.64	$259.65	$259.60
Purchase #4	$133.92	3.270%	$138.2992	$138.30	$138.30	$138.30
Purchase #5	$59.34	13.249%	$67.202	$67.20	$67.20	$67.20
Purchase #6	$19.82	13.846%	$22.5643	$22.56	$22.55	$22.60
Purchase #7	$93.47	11.117%	$103.8611	$103.86	$103.85	$103.90
7 purchase totals =	$765.81		$836.4568	$836.45	$836.45	$836.50