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	$6.64	6.311%	$7.0591	$7.06	$7.05	$7.10
Purchase #2	$76.62	8.551%	$83.1718	$83.17	$83.15	$83.20
Purchase #3	$139.74	3.628%	$144.8098	$144.81	$144.80	$144.80
Purchase #4	$103.92	12.184%	$116.5816	$116.58	$116.60	$116.60
Purchase #5	$233.58	11.283%	$259.9348	$259.93	$259.95	$259.90
Purchase #6	$37.73	12.600%	$42.484	$42.48	$42.50	$42.50
Purchase #7	$29.88	8.347%	$32.3741	$32.37	$32.35	$32.40
7 purchase totals =	$628.11		$686.4152	$686.40	$686.40	$686.50