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	$239.59	7.108%	$256.6201	$256.62	$256.60	$256.60
Purchase #2	$219.94	13.773%	$250.2323	$250.23	$250.25	$250.20
Purchase #3	$165.84	9.726%	$181.9696	$181.97	$181.95	$182.00
Purchase #4	$173.44	10.827%	$192.2183	$192.22	$192.20	$192.20
Purchase #5	$29.31	9.202%	$32.0071	$32.01	$32.00	$32.00
Purchase #6	$79.58	12.703%	$89.689	$89.69	$89.70	$89.70
Purchase #7	$38.57	9.867%	$42.3757	$42.38	$42.40	$42.40
7 purchase totals =	$946.27		$1,045.1121	$1,045.12	$1,045.10	$1,045.10