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	$37.86	13.379%	$42.9253	$42.93	$42.95	$42.90
Purchase #2	$70.86	3.280%	$73.1842	$73.18	$73.20	$73.20
Purchase #3	$25.97	12.431%	$29.1983	$29.20	$29.20	$29.20
Purchase #4	$106.66	9.567%	$116.8642	$116.86	$116.85	$116.90
Purchase #5	$89.98	11.635%	$100.4492	$100.45	$100.45	$100.40
Purchase #6	$147.31	7.665%	$158.6013	$158.60	$158.60	$158.60
Purchase #7	$155.31	3.505%	$160.7536	$160.75	$160.75	$160.80
7 purchase totals =	$633.95		$681.9761	$681.97	$682.00	$682.00