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	$50.52	8.306%	$54.7162	$54.72	$54.70	$54.70
Purchase #2	$50.76	11.864%	$56.7822	$56.78	$56.80	$56.80
Purchase #3	$52.60	10.122%	$57.9242	$57.92	$57.90	$57.90
Purchase #4	$198.39	7.270%	$212.813	$212.81	$212.80	$212.80
Purchase #5	$152.50	5.342%	$160.6466	$160.65	$160.65	$160.60
Purchase #6	$213.41	4.710%	$223.4616	$223.46	$223.45	$223.50
Purchase #7	$176.41	7.401%	$189.4661	$189.47	$189.45	$189.50
7 purchase totals =	$894.59		$955.8099	$955.81	$955.75	$955.80