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	$212.57	9.302%	$232.3433	$232.34	$232.35	$232.30
Purchase #2	$126.62	10.858%	$140.3684	$140.37	$140.35	$140.40
Purchase #3	$91.90	12.500%	$103.3875	$103.39	$103.40	$103.40
Purchase #4	$163.73	10.790%	$181.3965	$181.40	$181.40	$181.40
Purchase #5	$111.94	5.751%	$118.3777	$118.38	$118.40	$118.40
Purchase #6	$70.35	11.268%	$78.277	$78.28	$78.30	$78.30
Purchase #7	$20.50	3.513%	$21.2202	$21.22	$21.20	$21.20
7 purchase totals =	$797.61		$875.3706	$875.38	$875.40	$875.40