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	$89.60	11.502%	$99.9058	$99.91	$99.90	$99.90
Purchase #2	$107.86	4.477%	$112.6889	$112.69	$112.70	$112.70
Purchase #3	$5.74	3.685%	$5.9515	$5.95	$5.95	$6.00
Purchase #4	$104.56	8.859%	$113.823	$113.82	$113.80	$113.80
Purchase #5	$102.84	6.301%	$109.3199	$109.32	$109.30	$109.30
Purchase #6	$21.76	9.864%	$23.9064	$23.91	$23.90	$23.90
Purchase #7	$99.25	6.276%	$105.4789	$105.48	$105.50	$105.50
7 purchase totals =	$531.61		$571.0744	$571.08	$571.05	$571.10