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	$53.38	12.112%	$59.8454	$59.85	$59.85	$59.80
Purchase #2	$102.85	7.638%	$110.7057	$110.71	$110.70	$110.70
Purchase #3	$58.81	4.734%	$61.5941	$61.59	$61.60	$61.60
Purchase #4	$91.90	7.409%	$98.7089	$98.71	$98.70	$98.70
Purchase #5	$62.44	8.749%	$67.9029	$67.90	$67.90	$67.90
Purchase #6	$143.38	5.397%	$151.1182	$151.12	$151.10	$151.10
Purchase #7	$87.68	11.667%	$97.9096	$97.91	$97.90	$97.90
7 purchase totals =	$600.44		$647.7848	$647.79	$647.75	$647.70