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	$11.39	9.851%	$12.512	$12.51	$12.50	$12.50
Purchase #2	$103.96	7.366%	$111.6177	$111.62	$111.60	$111.60
Purchase #3	$160.39	6.662%	$171.0752	$171.08	$171.10	$171.10
Purchase #4	$243.27	9.179%	$265.5998	$265.60	$265.60	$265.60
Purchase #5	$119.33	5.409%	$125.7846	$125.78	$125.80	$125.80
Purchase #6	$116.31	9.658%	$127.5432	$127.54	$127.55	$127.50
Purchase #7	$217.50	4.736%	$227.8008	$227.80	$227.80	$227.80
7 purchase totals =	$972.15		$1,041.9333	$1,041.93	$1,041.95	$1,041.90