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	$13.80	12.454%	$15.5187	$15.52	$15.50	$15.50
Purchase #2	$75.99	11.345%	$84.6111	$84.61	$84.60	$84.60
Purchase #3	$169.98	12.797%	$191.7323	$191.73	$191.75	$191.70
Purchase #4	$81.89	9.680%	$89.817	$89.82	$89.80	$89.80
Purchase #5	$243.99	5.276%	$256.8629	$256.86	$256.85	$256.90
Purchase #6	$144.95	7.772%	$156.2155	$156.22	$156.20	$156.20
Purchase #7	$57.50	5.850%	$60.8638	$60.86	$60.85	$60.90
7 purchase totals =	$788.10		$855.6213	$855.62	$855.55	$855.60