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	$133.81	9.386%	$146.3694	$146.37	$146.35	$146.40
Purchase #2	$108.54	7.638%	$116.8303	$116.83	$116.85	$116.80
Purchase #3	$190.48	8.368%	$206.4194	$206.42	$206.40	$206.40
Purchase #4	$84.54	5.653%	$89.319	$89.32	$89.30	$89.30
Purchase #5	$168.52	7.382%	$180.9601	$180.96	$180.95	$181.00
Purchase #6	$75.53	3.726%	$78.3442	$78.34	$78.35	$78.30
Purchase #7	$113.29	12.873%	$127.8738	$127.87	$127.85	$127.90
7 purchase totals =	$874.71		$946.1162	$946.11	$946.05	$946.10