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	$116.64	3.619%	$120.8612	$120.86	$120.85	$120.90
Purchase #2	$191.97	12.579%	$216.1179	$216.12	$216.10	$216.10
Purchase #3	$99.46	8.719%	$108.1319	$108.13	$108.15	$108.10
Purchase #4	$83.77	6.616%	$89.3122	$89.31	$89.30	$89.30
Purchase #5	$40.79	4.670%	$42.6949	$42.69	$42.70	$42.70
Purchase #6	$15.50	7.389%	$16.6453	$16.65	$16.65	$16.60
Purchase #7	$204.67	8.489%	$222.0444	$222.04	$222.05	$222.00
7 purchase totals =	$752.80		$815.8078	$815.80	$815.80	$815.70