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	$38.85	3.432%	$40.1833	$40.18	$40.20	$40.20
Purchase #2	$234.60	9.298%	$256.4131	$256.41	$256.40	$256.40
Purchase #3	$218.78	9.441%	$239.435	$239.44	$239.45	$239.40
Purchase #4	$43.68	7.190%	$46.8206	$46.82	$46.80	$46.80
Purchase #5	$113.59	11.838%	$127.0368	$127.04	$127.05	$127.00
Purchase #6	$45.61	4.233%	$47.5407	$47.54	$47.55	$47.50
Purchase #7	$221.55	10.762%	$245.3932	$245.39	$245.40	$245.40
7 purchase totals =	$916.66		$1,002.8227	$1,002.82	$1,002.85	$1,002.70