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	$102.86	5.382%	$108.3959	$108.40	$108.40	$108.40
Purchase #2	$71.27	5.304%	$75.0502	$75.05	$75.05	$75.10
Purchase #3	$18.87	13.774%	$21.4692	$21.47	$21.45	$21.50
Purchase #4	$45.81	11.598%	$51.123	$51.12	$51.10	$51.10
Purchase #5	$50.66	7.633%	$54.5269	$54.53	$54.55	$54.50
Purchase #6	$32.34	3.382%	$33.4337	$33.43	$33.45	$33.40
Purchase #7	$133.31	6.155%	$141.5152	$141.52	$141.50	$141.50
7 purchase totals =	$455.12		$485.5141	$485.52	$485.50	$485.50