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	$5.51	5.223%	$5.7978	$5.80	$5.80	$5.80
Purchase #2	$133.69	5.782%	$141.42	$141.42	$141.40	$141.40
Purchase #3	$150.79	11.731%	$168.4792	$168.48	$168.50	$168.50
Purchase #4	$110.33	12.117%	$123.6987	$123.70	$123.70	$123.70
Purchase #5	$73.39	12.856%	$82.825	$82.83	$82.85	$82.80
Purchase #6	$81.91	6.691%	$87.3906	$87.39	$87.40	$87.40
Purchase #7	$67.81	3.232%	$70.0016	$70.00	$70.00	$70.00
7 purchase totals =	$623.43		$679.6129	$679.62	$679.65	$679.60