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	$244.53	4.327%	$255.1108	$255.11	$255.10	$255.10
Purchase #2	$72.38	9.802%	$79.4747	$79.47	$79.45	$79.50
Purchase #3	$133.64	13.134%	$151.1923	$151.19	$151.20	$151.20
Purchase #4	$38.83	12.267%	$43.5933	$43.59	$43.60	$43.60
Purchase #5	$116.71	6.266%	$124.023	$124.02	$124.00	$124.00
Purchase #6	$180.37	7.221%	$193.3945	$193.39	$193.40	$193.40
Purchase #7	$100.77	8.736%	$109.5733	$109.57	$109.55	$109.60
7 purchase totals =	$887.23		$956.3619	$956.34	$956.30	$956.40