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	$46.70	11.735%	$52.1802	$52.18	$52.20	$52.20
Purchase #2	$38.73	12.164%	$43.4411	$43.44	$43.45	$43.40
Purchase #3	$209.41	8.552%	$227.3187	$227.32	$227.30	$227.30
Purchase #4	$151.29	4.125%	$157.5307	$157.53	$157.55	$157.50
Purchase #5	$36.88	4.570%	$38.5654	$38.57	$38.55	$38.60
Purchase #6	$55.32	6.660%	$59.0043	$59.00	$59.00	$59.00
Purchase #7	$164.57	4.594%	$172.1303	$172.13	$172.15	$172.10
7 purchase totals =	$702.90		$750.1707	$750.17	$750.20	$750.10