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	$238.96	3.578%	$247.51	$247.51	$247.50	$247.50
Purchase #2	$233.96	11.150%	$260.0465	$260.05	$260.05	$260.00
Purchase #3	$112.41	13.511%	$127.5977	$127.60	$127.60	$127.60
Purchase #4	$114.26	6.662%	$121.872	$121.87	$121.85	$121.90
Purchase #5	$90.72	5.516%	$95.7241	$95.72	$95.70	$95.70
Purchase #6	$80.52	3.443%	$83.2923	$83.29	$83.30	$83.30
Purchase #7	$161.47	12.807%	$182.1495	$182.15	$182.15	$182.10
7 purchase totals =	$1,032.30		$1,118.1921	$1,118.19	$1,118.15	$1,118.10