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	$187.40	11.695%	$209.3164	$209.32	$209.30	$209.30
Purchase #2	$238.62	12.801%	$269.1657	$269.17	$269.15	$269.20
Purchase #3	$185.92	13.138%	$210.3462	$210.35	$210.35	$210.30
Purchase #4	$108.61	4.807%	$113.8309	$113.83	$113.85	$113.80
Purchase #5	$136.59	5.626%	$144.2746	$144.27	$144.25	$144.30
Purchase #6	$109.39	10.274%	$120.6287	$120.63	$120.65	$120.60
Purchase #7	$79.75	4.647%	$83.456	$83.46	$83.45	$83.50
7 purchase totals =	$1,046.28		$1,151.0185	$1,151.03	$1,151.00	$1,151.00