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	$26.30	4.427%	$27.4643	$27.46	$27.45	$27.50
Purchase #2	$17.57	13.225%	$19.8936	$19.89	$19.90	$19.90
Purchase #3	$174.47	7.720%	$187.9391	$187.94	$187.95	$187.90
Purchase #4	$33.65	11.803%	$37.6217	$37.62	$37.60	$37.60
Purchase #5	$7.89	4.548%	$8.2488	$8.25	$8.25	$8.20
Purchase #6	$88.90	7.522%	$95.5871	$95.59	$95.60	$95.60
Purchase #7	$67.52	3.749%	$70.0513	$70.05	$70.05	$70.10
7 purchase totals =	$416.30		$446.8059	$446.80	$446.80	$446.80