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	$20.81	5.213%	$21.8948	$21.89	$21.90	$21.90
Purchase #2	$56.85	11.641%	$63.4679	$63.47	$63.45	$63.50
Purchase #3	$108.50	3.283%	$112.0621	$112.06	$112.05	$112.10
Purchase #4	$99.85	11.230%	$111.0632	$111.06	$111.05	$111.10
Purchase #5	$225.90	6.294%	$240.1181	$240.12	$240.10	$240.10
Purchase #6	$167.49	13.306%	$189.7762	$189.78	$189.80	$189.80
Purchase #7	$235.73	11.486%	$262.8059	$262.81	$262.80	$262.80
7 purchase totals =	$915.13		$1,001.1882	$1,001.19	$1,001.15	$1,001.30