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	$49.44	7.516%	$53.1559	$53.16	$53.15	$53.20
Purchase #2	$184.98	11.527%	$206.3026	$206.30	$206.30	$206.30
Purchase #3	$103.76	9.466%	$113.5819	$113.58	$113.60	$113.60
Purchase #4	$171.87	8.185%	$185.9376	$185.94	$185.95	$185.90
Purchase #5	$59.38	12.867%	$67.0204	$67.02	$67.00	$67.00
Purchase #6	$102.93	11.198%	$114.4561	$114.46	$114.45	$114.50
Purchase #7	$92.46	7.438%	$99.3372	$99.34	$99.35	$99.30
7 purchase totals =	$764.82		$839.7917	$839.80	$839.80	$839.80