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	$29.42	10.840%	$32.6091	$32.61	$32.60	$32.60
Purchase #2	$209.92	13.337%	$237.917	$237.92	$237.90	$237.90
Purchase #3	$245.75	13.321%	$278.4864	$278.49	$278.50	$278.50
Purchase #4	$82.49	9.853%	$90.6177	$90.62	$90.60	$90.60
Purchase #5	$138.96	11.423%	$154.8334	$154.83	$154.85	$154.80
Purchase #6	$32.89	7.802%	$35.4561	$35.46	$35.45	$35.50
Purchase #7	$109.73	4.700%	$114.8873	$114.89	$114.90	$114.90
7 purchase totals =	$849.16		$944.8070	$944.82	$944.80	$944.80