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	$81.79	6.159%	$86.8274	$86.83	$86.85	$86.80
Purchase #2	$18.92	9.855%	$20.7846	$20.78	$20.80	$20.80
Purchase #3	$223.84	6.538%	$238.4747	$238.47	$238.45	$238.50
Purchase #4	$246.56	7.308%	$264.5786	$264.58	$264.60	$264.60
Purchase #5	$82.90	9.443%	$90.7282	$90.73	$90.75	$90.70
Purchase #6	$148.28	7.558%	$159.487	$159.49	$159.50	$159.50
Purchase #7	$172.51	3.191%	$178.0148	$178.01	$178.00	$178.00
7 purchase totals =	$974.80		$1,038.8953	$1,038.89	$1,038.95	$1,038.90