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	$80.34	11.606%	$89.6643	$89.66	$89.65	$89.70
Purchase #2	$19.92	7.771%	$21.468	$21.47	$21.45	$21.50
Purchase #3	$141.46	4.538%	$147.8795	$147.88	$147.90	$147.90
Purchase #4	$202.86	8.848%	$220.8091	$220.81	$220.80	$220.80
Purchase #5	$211.76	11.110%	$235.2865	$235.29	$235.30	$235.30
Purchase #6	$76.39	3.232%	$78.8589	$78.86	$78.85	$78.90
Purchase #7	$52.43	10.730%	$58.0557	$58.06	$58.05	$58.10
7 purchase totals =	$785.16		$852.0220	$852.03	$852.00	$852.20