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	$160.87	12.698%	$181.2973	$181.30	$181.30	$181.30
Purchase #2	$185.53	13.631%	$210.8196	$210.82	$210.80	$210.80
Purchase #3	$226.56	5.420%	$238.8396	$238.84	$238.85	$238.80
Purchase #4	$6.73	11.156%	$7.4808	$7.48	$7.50	$7.50
Purchase #5	$132.38	3.166%	$136.5712	$136.57	$136.55	$136.60
Purchase #6	$56.63	4.556%	$59.2101	$59.21	$59.20	$59.20
Purchase #7	$120.95	5.681%	$127.8212	$127.82	$127.80	$127.80
7 purchase totals =	$889.65		$962.0398	$962.04	$962.00	$962.00