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	$223.91	11.837%	$250.4142	$250.41	$250.40	$250.40
Purchase #2	$148.78	13.302%	$168.5707	$168.57	$168.55	$168.60
Purchase #3	$173.29	7.660%	$186.564	$186.56	$186.55	$186.60
Purchase #4	$39.95	9.387%	$43.7001	$43.70	$43.70	$43.70
Purchase #5	$95.72	6.417%	$101.8624	$101.86	$101.85	$101.90
Purchase #6	$66.69	9.306%	$72.8962	$72.90	$72.90	$72.90
Purchase #7	$149.81	11.222%	$166.6217	$166.62	$166.60	$166.60
7 purchase totals =	$898.15		$990.6293	$990.62	$990.55	$990.70