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	$202.28	9.814%	$222.1318	$222.13	$222.15	$222.10
Purchase #2	$75.40	12.865%	$85.1002	$85.10	$85.10	$85.10
Purchase #3	$95.38	12.679%	$107.4732	$107.47	$107.45	$107.50
Purchase #4	$109.60	12.748%	$123.5718	$123.57	$123.55	$123.60
Purchase #5	$135.66	4.749%	$142.1025	$142.10	$142.10	$142.10
Purchase #6	$36.80	7.615%	$39.6023	$39.60	$39.60	$39.60
Purchase #7	$74.59	9.714%	$81.8357	$81.84	$81.85	$81.80
7 purchase totals =	$729.71		$801.8175	$801.81	$801.80	$801.80