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	$155.53	7.700%	$167.5058	$167.51	$167.50	$167.50
Purchase #2	$174.59	13.720%	$198.5437	$198.54	$198.55	$198.50
Purchase #3	$147.59	11.466%	$164.5127	$164.51	$164.50	$164.50
Purchase #4	$83.99	10.298%	$92.6393	$92.64	$92.65	$92.60
Purchase #5	$32.60	11.589%	$36.378	$36.38	$36.40	$36.40
Purchase #6	$89.53	7.226%	$95.9994	$96.00	$96.00	$96.00
Purchase #7	$217.73	7.217%	$233.4436	$233.44	$233.45	$233.40
7 purchase totals =	$901.56		$989.0225	$989.02	$989.05	$988.90