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	$218.73	4.854%	$229.3472	$229.35	$229.35	$229.30
Purchase #2	$72.59	13.613%	$82.4717	$82.47	$82.45	$82.50
Purchase #3	$187.86	11.294%	$209.0769	$209.08	$209.10	$209.10
Purchase #4	$197.82	9.595%	$216.8008	$216.80	$216.80	$216.80
Purchase #5	$95.49	11.345%	$106.3233	$106.32	$106.30	$106.30
Purchase #6	$34.46	10.457%	$38.0635	$38.06	$38.05	$38.10
Purchase #7	$108.57	7.267%	$116.4598	$116.46	$116.45	$116.50
7 purchase totals =	$915.52		$998.5432	$998.54	$998.50	$998.60