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	$133.87	4.492%	$139.8834	$139.88	$139.90	$139.90
Purchase #2	$105.73	13.296%	$119.7879	$119.79	$119.80	$119.80
Purchase #3	$88.78	12.483%	$99.8624	$99.86	$99.85	$99.90
Purchase #4	$190.50	10.787%	$211.0492	$211.05	$211.05	$211.00
Purchase #5	$175.81	3.300%	$181.6117	$181.61	$181.60	$181.60
Purchase #6	$215.63	10.332%	$237.9089	$237.91	$237.90	$237.90
Purchase #7	$53.70	7.477%	$57.7151	$57.72	$57.70	$57.70
7 purchase totals =	$964.02		$1,047.8186	$1,047.82	$1,047.80	$1,047.80