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	$77.67	8.703%	$84.4296	$84.43	$84.45	$84.40
Purchase #2	$215.84	11.474%	$240.6055	$240.61	$240.60	$240.60
Purchase #3	$118.70	7.151%	$127.1882	$127.19	$127.20	$127.20
Purchase #4	$35.44	8.772%	$38.5488	$38.55	$38.55	$38.50
Purchase #5	$147.48	13.271%	$167.0521	$167.05	$167.05	$167.10
Purchase #6	$44.51	8.630%	$48.3512	$48.35	$48.35	$48.40
Purchase #7	$83.56	7.553%	$89.8713	$89.87	$89.85	$89.90
7 purchase totals =	$723.20		$796.0467	$796.05	$796.05	$796.10