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	$53.89	5.354%	$56.7753	$56.78	$56.80	$56.80
Purchase #2	$155.54	6.590%	$165.7901	$165.79	$165.80	$165.80
Purchase #3	$114.32	4.750%	$119.7502	$119.75	$119.75	$119.80
Purchase #4	$45.98	9.229%	$50.2235	$50.22	$50.20	$50.20
Purchase #5	$81.87	8.221%	$88.6005	$88.60	$88.60	$88.60
Purchase #6	$142.49	9.517%	$156.0508	$156.05	$156.05	$156.10
Purchase #7	$62.73	6.722%	$66.9467	$66.95	$66.95	$66.90
7 purchase totals =	$656.82		$704.1371	$704.14	$704.15	$704.20