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	$61.77	13.440%	$70.0719	$70.07	$70.05	$70.10
Purchase #2	$164.63	6.447%	$175.2437	$175.24	$175.25	$175.20
Purchase #3	$159.67	10.223%	$175.9931	$175.99	$176.00	$176.00
Purchase #4	$154.70	11.704%	$172.8061	$172.81	$172.80	$172.80
Purchase #5	$165.77	11.446%	$184.744	$184.74	$184.75	$184.70
Purchase #6	$55.71	7.492%	$59.8838	$59.88	$59.90	$59.90
Purchase #7	$78.59	4.112%	$81.8216	$81.82	$81.80	$81.80
7 purchase totals =	$840.84		$920.5642	$920.55	$920.55	$920.50