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	$46.60	13.274%	$52.7857	$52.79	$52.80	$52.80
Purchase #2	$64.78	4.108%	$67.4412	$67.44	$67.45	$67.40
Purchase #3	$222.85	10.663%	$246.6125	$246.61	$246.60	$246.60
Purchase #4	$60.48	10.851%	$67.0427	$67.04	$67.05	$67.00
Purchase #5	$132.62	3.348%	$137.0601	$137.06	$137.05	$137.10
Purchase #6	$164.32	12.412%	$184.7154	$184.72	$184.70	$184.70
Purchase #7	$30.25	10.165%	$33.3249	$33.32	$33.30	$33.30
7 purchase totals =	$721.90		$788.9825	$788.98	$788.95	$788.90