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	$91.62	9.652%	$100.4632	$100.46	$100.45	$100.50
Purchase #2	$72.58	12.619%	$81.7389	$81.74	$81.75	$81.70
Purchase #3	$138.45	4.500%	$144.6803	$144.68	$144.70	$144.70
Purchase #4	$230.48	12.583%	$259.4813	$259.48	$259.50	$259.50
Purchase #5	$73.41	9.147%	$80.1248	$80.12	$80.10	$80.10
Purchase #6	$83.36	4.716%	$87.2913	$87.29	$87.30	$87.30
Purchase #7	$209.37	6.209%	$222.3698	$222.37	$222.35	$222.40
7 purchase totals =	$899.27		$976.1496	$976.14	$976.15	$976.20