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	$120.62	4.608%	$126.1782	$126.18	$126.20	$126.20
Purchase #2	$230.94	11.153%	$256.6967	$256.70	$256.70	$256.70
Purchase #3	$103.87	7.714%	$111.8825	$111.88	$111.90	$111.90
Purchase #4	$99.28	4.397%	$103.6453	$103.65	$103.65	$103.60
Purchase #5	$38.38	11.287%	$42.712	$42.71	$42.70	$42.70
Purchase #6	$214.35	3.260%	$221.3378	$221.34	$221.35	$221.30
Purchase #7	$29.36	7.319%	$31.5089	$31.51	$31.50	$31.50
7 purchase totals =	$836.80		$893.9614	$893.97	$894.00	$893.90