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	$40.48	5.831%	$42.8404	$42.84	$42.85	$42.80
Purchase #2	$124.59	4.253%	$129.8888	$129.89	$129.90	$129.90
Purchase #3	$150.78	13.691%	$171.4233	$171.42	$171.40	$171.40
Purchase #4	$155.99	9.666%	$171.068	$171.07	$171.05	$171.10
Purchase #5	$65.96	7.517%	$70.9182	$70.92	$70.90	$70.90
Purchase #6	$26.58	3.288%	$27.454	$27.45	$27.45	$27.50
Purchase #7	$62.28	13.700%	$70.8124	$70.81	$70.80	$70.80
7 purchase totals =	$626.66		$684.4051	$684.40	$684.35	$684.40