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	$133.56	3.599%	$138.3668	$138.37	$138.35	$138.40
Purchase #2	$166.89	10.759%	$184.8457	$184.85	$184.85	$184.80
Purchase #3	$210.82	6.323%	$224.1501	$224.15	$224.15	$224.20
Purchase #4	$77.46	6.668%	$82.625	$82.63	$82.65	$82.60
Purchase #5	$204.26	6.253%	$217.0324	$217.03	$217.05	$217.00
Purchase #6	$158.89	9.755%	$174.3897	$174.39	$174.40	$174.40
Purchase #7	$45.37	12.738%	$51.1492	$51.15	$51.15	$51.10
7 purchase totals =	$997.25		$1,072.5589	$1,072.57	$1,072.60	$1,072.50