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	$92.66	4.255%	$96.6027	$96.60	$96.60	$96.60
Purchase #2	$81.27	10.730%	$89.9903	$89.99	$90.00	$90.00
Purchase #3	$166.71	8.294%	$180.5369	$180.54	$180.55	$180.50
Purchase #4	$12.86	7.533%	$13.8287	$13.83	$13.85	$13.80
Purchase #5	$61.47	10.366%	$67.842	$67.84	$67.85	$67.80
Purchase #6	$170.30	13.240%	$192.8477	$192.85	$192.85	$192.80
Purchase #7	$53.29	4.204%	$55.5303	$55.53	$55.55	$55.50
7 purchase totals =	$638.56		$697.1786	$697.18	$697.25	$697.00