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	$171.98	10.143%	$189.4239	$189.42	$189.40	$189.40
Purchase #2	$82.47	8.220%	$89.249	$89.25	$89.25	$89.20
Purchase #3	$247.81	5.795%	$262.1706	$262.17	$262.15	$262.20
Purchase #4	$190.91	3.508%	$197.6071	$197.61	$197.60	$197.60
Purchase #5	$64.25	13.135%	$72.6892	$72.69	$72.70	$72.70
Purchase #6	$22.44	8.818%	$24.4188	$24.42	$24.40	$24.40
Purchase #7	$127.47	13.855%	$145.131	$145.13	$145.15	$145.10
7 purchase totals =	$907.33		$980.6896	$980.69	$980.65	$980.60