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	$101.73	4.648%	$106.4584	$106.46	$106.45	$106.50
Purchase #2	$218.67	10.493%	$241.615	$241.62	$241.60	$241.60
Purchase #3	$128.32	13.598%	$145.769	$145.77	$145.75	$145.80
Purchase #4	$109.52	12.459%	$123.1651	$123.17	$123.15	$123.20
Purchase #5	$113.56	5.817%	$120.1658	$120.17	$120.15	$120.20
Purchase #6	$67.87	6.789%	$72.4777	$72.48	$72.50	$72.50
Purchase #7	$75.70	10.678%	$83.7832	$83.78	$83.80	$83.80
7 purchase totals =	$815.37		$893.4342	$893.45	$893.40	$893.60