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	$44.38	5.477%	$46.8107	$46.81	$46.80	$46.80
Purchase #2	$136.83	7.306%	$146.8268	$146.83	$146.85	$146.80
Purchase #3	$157.97	4.345%	$164.8338	$164.83	$164.85	$164.80
Purchase #4	$224.47	13.668%	$255.1506	$255.15	$255.15	$255.20
Purchase #5	$81.33	12.281%	$91.3181	$91.32	$91.30	$91.30
Purchase #6	$62.29	7.666%	$67.0652	$67.07	$67.05	$67.10
Purchase #7	$54.95	11.535%	$61.2885	$61.29	$61.30	$61.30
7 purchase totals =	$762.22		$833.2937	$833.30	$833.30	$833.30