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	$136.57	13.337%	$154.7843	$154.78	$154.80	$154.80
Purchase #2	$249.80	10.658%	$276.4237	$276.42	$276.40	$276.40
Purchase #3	$180.92	8.803%	$196.8464	$196.85	$196.85	$196.80
Purchase #4	$96.87	3.729%	$100.4823	$100.48	$100.50	$100.50
Purchase #5	$153.43	6.583%	$163.5303	$163.53	$163.55	$163.50
Purchase #6	$174.76	10.414%	$192.9595	$192.96	$192.95	$193.00
Purchase #7	$67.43	7.438%	$72.4454	$72.45	$72.45	$72.40
7 purchase totals =	$1,059.78		$1,157.4719	$1,157.47	$1,157.50	$1,157.40