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	$94.90	4.335%	$99.0139	$99.01	$99.00	$99.00
Purchase #2	$27.79	11.596%	$31.0125	$31.01	$31.00	$31.00
Purchase #3	$191.60	13.400%	$217.2744	$217.27	$217.25	$217.30
Purchase #4	$120.89	8.408%	$131.0544	$131.05	$131.05	$131.10
Purchase #5	$149.42	11.418%	$166.4808	$166.48	$166.50	$166.50
Purchase #6	$13.90	13.626%	$15.794	$15.79	$15.80	$15.80
Purchase #7	$180.60	4.256%	$188.2863	$188.29	$188.30	$188.30
7 purchase totals =	$779.10		$848.9163	$848.90	$848.90	$849.00