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	$90.82	10.716%	$100.5523	$100.55	$100.55	$100.60
Purchase #2	$119.39	11.685%	$133.3407	$133.34	$133.35	$133.30
Purchase #3	$117.43	11.571%	$131.0178	$131.02	$131.00	$131.00
Purchase #4	$18.54	9.518%	$20.3046	$20.30	$20.30	$20.30
Purchase #5	$19.74	11.780%	$22.0654	$22.07	$22.05	$22.10
Purchase #6	$38.53	4.255%	$40.1695	$40.17	$40.15	$40.20
Purchase #7	$159.38	9.320%	$174.2342	$174.23	$174.25	$174.20
7 purchase totals =	$563.83		$621.6845	$621.68	$621.65	$621.70