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	$12.31	6.168%	$13.0693	$13.07	$13.05	$13.10
Purchase #2	$242.31	10.508%	$267.7719	$267.77	$267.75	$267.80
Purchase #3	$86.97	6.558%	$92.6735	$92.67	$92.65	$92.70
Purchase #4	$136.89	4.395%	$142.9063	$142.91	$142.90	$142.90
Purchase #5	$200.58	8.345%	$217.3184	$217.32	$217.30	$217.30
Purchase #6	$96.57	13.693%	$109.7933	$109.79	$109.80	$109.80
Purchase #7	$229.61	3.278%	$237.1366	$237.14	$237.15	$237.10
7 purchase totals =	$1,005.24		$1,080.6693	$1,080.67	$1,080.60	$1,080.70