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	$74.51	5.485%	$78.5969	$78.60	$78.60	$78.60
Purchase #2	$34.81	13.115%	$39.3753	$39.38	$39.40	$39.40
Purchase #3	$35.84	4.257%	$37.3657	$37.37	$37.35	$37.40
Purchase #4	$145.86	12.482%	$164.0662	$164.07	$164.05	$164.10
Purchase #5	$112.64	10.208%	$124.1383	$124.14	$124.15	$124.10
Purchase #6	$99.91	3.451%	$103.3579	$103.36	$103.35	$103.40
Purchase #7	$125.89	4.319%	$131.3272	$131.33	$131.35	$131.30
7 purchase totals =	$629.46		$678.2275	$678.25	$678.25	$678.30