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	$64.89	12.373%	$72.9188	$72.92	$72.90	$72.90
Purchase #2	$80.62	11.134%	$89.5962	$89.60	$89.60	$89.60
Purchase #3	$60.57	4.287%	$63.1666	$63.17	$63.15	$63.20
Purchase #4	$21.57	3.275%	$22.2764	$22.28	$22.30	$22.30
Purchase #5	$63.37	13.603%	$71.9902	$71.99	$72.00	$72.00
Purchase #6	$132.81	3.170%	$137.0201	$137.02	$137.00	$137.00
Purchase #7	$96.95	6.129%	$102.8921	$102.89	$102.90	$102.90
7 purchase totals =	$520.78		$559.8604	$559.87	$559.85	$559.90