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	$239.77	9.786%	$263.2339	$263.23	$263.25	$263.20
Purchase #2	$90.69	6.129%	$96.2484	$96.25	$96.25	$96.20
Purchase #3	$226.50	7.757%	$244.0696	$244.07	$244.05	$244.10
Purchase #4	$59.73	5.285%	$62.8867	$62.89	$62.90	$62.90
Purchase #5	$31.43	13.762%	$35.7554	$35.76	$35.75	$35.80
Purchase #6	$41.49	8.655%	$45.081	$45.08	$45.10	$45.10
Purchase #7	$86.50	9.301%	$94.5454	$94.55	$94.55	$94.50
7 purchase totals =	$776.11		$841.8204	$841.83	$841.85	$841.80