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	$115.90	7.771%	$124.9066	$124.91	$124.90	$124.90
Purchase #2	$210.73	8.388%	$228.406	$228.41	$228.40	$228.40
Purchase #3	$201.60	13.267%	$228.3463	$228.35	$228.35	$228.30
Purchase #4	$29.49	6.228%	$31.3266	$31.33	$31.35	$31.30
Purchase #5	$153.44	13.724%	$174.4981	$174.50	$174.50	$174.50
Purchase #6	$144.79	3.786%	$150.2717	$150.27	$150.25	$150.30
Purchase #7	$89.97	12.838%	$101.5203	$101.52	$101.50	$101.50
7 purchase totals =	$945.92		$1,039.2756	$1,039.29	$1,039.25	$1,039.20