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	$101.66	4.763%	$106.5021	$106.50	$106.50	$106.50
Purchase #2	$90.59	10.575%	$100.1699	$100.17	$100.15	$100.20
Purchase #3	$53.62	10.379%	$59.1852	$59.19	$59.20	$59.20
Purchase #4	$155.60	12.282%	$174.7108	$174.71	$174.70	$174.70
Purchase #5	$32.36	7.474%	$34.7786	$34.78	$34.80	$34.80
Purchase #6	$14.29	3.460%	$14.7844	$14.78	$14.80	$14.80
Purchase #7	$56.90	4.658%	$59.5504	$59.55	$59.55	$59.60
7 purchase totals =	$505.02		$549.6814	$549.68	$549.70	$549.80