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	$30.78	3.328%	$31.8044	$31.80	$31.80	$31.80
Purchase #2	$171.98	5.278%	$181.0571	$181.06	$181.05	$181.10
Purchase #3	$116.37	6.459%	$123.8863	$123.89	$123.90	$123.90
Purchase #4	$20.95	7.254%	$22.4697	$22.47	$22.45	$22.50
Purchase #5	$119.28	11.775%	$133.3252	$133.33	$133.35	$133.30
Purchase #6	$105.56	4.741%	$110.5646	$110.56	$110.55	$110.60
Purchase #7	$172.68	4.510%	$180.4679	$180.47	$180.45	$180.50
7 purchase totals =	$737.60		$783.5752	$783.58	$783.55	$783.70