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	$69.71	10.662%	$77.1425	$77.14	$77.15	$77.10
Purchase #2	$13.33	10.237%	$14.6946	$14.69	$14.70	$14.70
Purchase #3	$118.71	3.717%	$123.1225	$123.12	$123.10	$123.10
Purchase #4	$90.89	5.385%	$95.7844	$95.78	$95.80	$95.80
Purchase #5	$108.41	3.780%	$112.5079	$112.51	$112.50	$112.50
Purchase #6	$6.76	9.490%	$7.4015	$7.40	$7.40	$7.40
Purchase #7	$110.89	13.689%	$126.0697	$126.07	$126.05	$126.10
7 purchase totals =	$518.70		$556.7231	$556.71	$556.70	$556.70