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	$40.76	3.121%	$42.0321	$42.03	$42.05	$42.00
Purchase #2	$174.60	9.573%	$191.3145	$191.31	$191.30	$191.30
Purchase #3	$96.36	7.195%	$103.2931	$103.29	$103.30	$103.30
Purchase #4	$111.25	6.541%	$118.5269	$118.53	$118.55	$118.50
Purchase #5	$33.62	8.684%	$36.5396	$36.54	$36.55	$36.50
Purchase #6	$30.48	12.741%	$34.3635	$34.36	$34.35	$34.40
Purchase #7	$91.29	11.142%	$101.4615	$101.46	$101.45	$101.50
7 purchase totals =	$578.36		$627.5312	$627.52	$627.55	$627.50