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	$89.89	12.479%	$101.1074	$101.11	$101.10	$101.10
Purchase #2	$65.27	8.156%	$70.5934	$70.59	$70.60	$70.60
Purchase #3	$73.45	12.238%	$82.4388	$82.44	$82.45	$82.40
Purchase #4	$229.43	12.619%	$258.3818	$258.38	$258.40	$258.40
Purchase #5	$113.39	7.705%	$122.1267	$122.13	$122.15	$122.10
Purchase #6	$123.66	4.685%	$129.4535	$129.45	$129.45	$129.50
Purchase #7	$35.40	13.392%	$40.1408	$40.14	$40.15	$40.10
7 purchase totals =	$730.49		$804.2424	$804.24	$804.30	$804.20