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	$79.97	11.476%	$89.1474	$89.15	$89.15	$89.10
Purchase #2	$126.44	3.863%	$131.3244	$131.32	$131.30	$131.30
Purchase #3	$126.69	11.570%	$141.348	$141.35	$141.35	$141.30
Purchase #4	$231.75	7.800%	$249.8265	$249.83	$249.85	$249.80
Purchase #5	$45.67	11.343%	$50.8503	$50.85	$50.85	$50.90
Purchase #6	$7.57	13.319%	$8.5782	$8.58	$8.60	$8.60
Purchase #7	$164.50	4.807%	$172.4075	$172.41	$172.40	$172.40
7 purchase totals =	$782.59		$843.4823	$843.49	$843.50	$843.40