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	$158.99	4.491%	$166.1302	$166.13	$166.15	$166.10
Purchase #2	$133.76	7.567%	$143.8816	$143.88	$143.90	$143.90
Purchase #3	$210.31	10.498%	$232.3883	$232.39	$232.40	$232.40
Purchase #4	$212.50	7.816%	$229.109	$229.11	$229.10	$229.10
Purchase #5	$42.78	13.407%	$48.5155	$48.52	$48.50	$48.50
Purchase #6	$106.25	9.435%	$116.2747	$116.27	$116.25	$116.30
Purchase #7	$196.67	11.258%	$218.8111	$218.81	$218.80	$218.80
7 purchase totals =	$1,061.26		$1,155.1104	$1,155.11	$1,155.10	$1,155.10