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	$74.89	7.258%	$80.3255	$80.33	$80.35	$80.30
Purchase #2	$45.90	7.365%	$49.2805	$49.28	$49.30	$49.30
Purchase #3	$151.90	4.274%	$158.3922	$158.39	$158.40	$158.40
Purchase #4	$54.70	4.696%	$57.2687	$57.27	$57.25	$57.30
Purchase #5	$213.52	11.234%	$237.5068	$237.51	$237.50	$237.50
Purchase #6	$60.70	10.544%	$67.1002	$67.10	$67.10	$67.10
Purchase #7	$43.69	10.787%	$48.4028	$48.40	$48.40	$48.40
7 purchase totals =	$645.30		$698.2767	$698.28	$698.30	$698.30