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	$193.76	5.584%	$204.5796	$204.58	$204.60	$204.60
Purchase #2	$117.62	12.714%	$132.5742	$132.57	$132.55	$132.60
Purchase #3	$218.25	9.138%	$238.1937	$238.19	$238.20	$238.20
Purchase #4	$86.33	4.465%	$90.1846	$90.18	$90.20	$90.20
Purchase #5	$248.73	12.536%	$279.9108	$279.91	$279.90	$279.90
Purchase #6	$88.89	10.610%	$98.3212	$98.32	$98.30	$98.30
Purchase #7	$170.40	11.345%	$189.7319	$189.73	$189.75	$189.70
7 purchase totals =	$1,123.98		$1,233.4960	$1,233.48	$1,233.50	$1,233.50