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	$227.85	6.823%	$243.3962	$243.40	$243.40	$243.40
Purchase #2	$49.99	5.649%	$52.8139	$52.81	$52.80	$52.80
Purchase #3	$24.89	5.616%	$26.2878	$26.29	$26.30	$26.30
Purchase #4	$244.50	8.337%	$264.884	$264.88	$264.90	$264.90
Purchase #5	$179.70	6.605%	$191.5692	$191.57	$191.55	$191.60
Purchase #6	$182.57	12.620%	$205.6103	$205.61	$205.60	$205.60
Purchase #7	$80.54	12.153%	$90.328	$90.33	$90.35	$90.30
7 purchase totals =	$990.04		$1,074.8894	$1,074.89	$1,074.90	$1,074.90