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	$204.32	6.301%	$217.1942	$217.19	$217.20	$217.20
Purchase #2	$185.27	4.199%	$193.0495	$193.05	$193.05	$193.00
Purchase #3	$130.95	10.311%	$144.4523	$144.45	$144.45	$144.50
Purchase #4	$120.96	5.299%	$127.3697	$127.37	$127.35	$127.40
Purchase #5	$76.74	7.544%	$82.5293	$82.53	$82.55	$82.50
Purchase #6	$89.55	10.807%	$99.2277	$99.23	$99.25	$99.20
Purchase #7	$23.56	12.714%	$26.5554	$26.56	$26.55	$26.60
7 purchase totals =	$831.35		$890.3781	$890.38	$890.40	$890.40