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	$246.70	9.582%	$270.3388	$270.34	$270.35	$270.30
Purchase #2	$52.62	13.259%	$59.5969	$59.60	$59.60	$59.60
Purchase #3	$135.40	11.537%	$151.0211	$151.02	$151.00	$151.00
Purchase #4	$191.29	3.556%	$198.0923	$198.09	$198.10	$198.10
Purchase #5	$73.81	6.219%	$78.4002	$78.40	$78.40	$78.40
Purchase #6	$73.47	6.351%	$78.1361	$78.14	$78.15	$78.10
Purchase #7	$27.79	4.487%	$29.0369	$29.04	$29.05	$29.00
7 purchase totals =	$801.08		$864.6223	$864.63	$864.65	$864.50