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	$80.64	7.315%	$86.5388	$86.54	$86.55	$86.50
Purchase #2	$33.93	12.460%	$38.1577	$38.16	$38.15	$38.20
Purchase #3	$133.39	13.792%	$151.7871	$151.79	$151.80	$151.80
Purchase #4	$82.51	3.769%	$85.6198	$85.62	$85.60	$85.60
Purchase #5	$52.88	4.309%	$55.1586	$55.16	$55.15	$55.20
Purchase #6	$135.95	9.223%	$148.4887	$148.49	$148.50	$148.50
Purchase #7	$220.51	6.622%	$235.1122	$235.11	$235.10	$235.10
7 purchase totals =	$739.81		$800.8629	$800.87	$800.85	$800.90