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	$19.89	3.379%	$20.5621	$20.56	$20.55	$20.60
Purchase #2	$51.47	9.540%	$56.3802	$56.38	$56.40	$56.40
Purchase #3	$54.72	13.757%	$62.2478	$62.25	$62.25	$62.20
Purchase #4	$5.33	10.674%	$5.8989	$5.90	$5.90	$5.90
Purchase #5	$52.63	10.249%	$58.024	$58.02	$58.00	$58.00
Purchase #6	$123.63	13.828%	$140.7256	$140.73	$140.75	$140.70
Purchase #7	$28.69	10.396%	$31.6726	$31.67	$31.65	$31.70
7 purchase totals =	$336.36		$375.5112	$375.51	$375.50	$375.50