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	$41.90	11.444%	$46.695	$46.70	$46.70	$46.70
Purchase #2	$10.98	12.840%	$12.3898	$12.39	$12.40	$12.40
Purchase #3	$177.81	11.870%	$198.916	$198.92	$198.90	$198.90
Purchase #4	$34.37	11.727%	$38.4006	$38.40	$38.40	$38.40
Purchase #5	$83.66	7.405%	$89.855	$89.86	$89.85	$89.90
Purchase #6	$39.83	9.420%	$43.582	$43.58	$43.60	$43.60
Purchase #7	$195.55	11.513%	$218.0637	$218.06	$218.05	$218.10
7 purchase totals =	$584.10		$647.9021	$647.91	$647.90	$648.00