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	$211.55	11.638%	$236.1702	$236.17	$236.15	$236.20
Purchase #2	$74.66	10.799%	$82.7225	$82.72	$82.70	$82.70
Purchase #3	$72.31	13.834%	$82.3134	$82.31	$82.30	$82.30
Purchase #4	$136.93	9.778%	$150.319	$150.32	$150.30	$150.30
Purchase #5	$133.96	3.105%	$138.1195	$138.12	$138.10	$138.10
Purchase #6	$237.28	13.231%	$268.6745	$268.67	$268.65	$268.70
Purchase #7	$21.56	4.652%	$22.563	$22.56	$22.55	$22.60
7 purchase totals =	$888.25		$980.8821	$980.87	$980.75	$980.90