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	$170.86	7.812%	$184.2076	$184.21	$184.20	$184.20
Purchase #2	$180.48	9.235%	$197.1473	$197.15	$197.15	$197.10
Purchase #3	$200.29	12.619%	$225.5646	$225.56	$225.55	$225.60
Purchase #4	$162.26	6.284%	$172.4564	$172.46	$172.45	$172.50
Purchase #5	$66.90	5.311%	$70.4531	$70.45	$70.45	$70.50
Purchase #6	$48.78	13.656%	$55.4414	$55.44	$55.45	$55.40
Purchase #7	$86.96	10.643%	$96.2152	$96.22	$96.20	$96.20
7 purchase totals =	$916.53		$1,001.4856	$1,001.49	$1,001.45	$1,001.50