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	$90.29	11.405%	$100.5876	$100.59	$100.60	$100.60
Purchase #2	$15.88	13.735%	$18.0611	$18.06	$18.05	$18.10
Purchase #3	$202.69	11.760%	$226.5263	$226.53	$226.55	$226.50
Purchase #4	$129.93	3.773%	$134.8323	$134.83	$134.85	$134.80
Purchase #5	$218.61	7.264%	$234.4898	$234.49	$234.50	$234.50
Purchase #6	$149.30	13.487%	$169.4361	$169.44	$169.45	$169.40
Purchase #7	$134.33	8.233%	$145.3894	$145.39	$145.40	$145.40
7 purchase totals =	$941.03		$1,029.3226	$1,029.33	$1,029.40	$1,029.30