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	$82.71	8.667%	$89.8785	$89.88	$89.90	$89.90
Purchase #2	$246.58	5.754%	$260.7682	$260.77	$260.75	$260.80
Purchase #3	$196.32	9.750%	$215.4612	$215.46	$215.45	$215.50
Purchase #4	$124.29	3.503%	$128.6439	$128.64	$128.65	$128.60
Purchase #5	$180.40	5.228%	$189.8313	$189.83	$189.85	$189.80
Purchase #6	$185.64	13.447%	$210.603	$210.60	$210.60	$210.60
Purchase #7	$225.56	3.444%	$233.3283	$233.33	$233.35	$233.30
7 purchase totals =	$1,241.50		$1,328.5144	$1,328.51	$1,328.55	$1,328.50