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	$13.95	13.847%	$15.8817	$15.88	$15.90	$15.90
Purchase #2	$85.74	12.532%	$96.4849	$96.48	$96.50	$96.50
Purchase #3	$160.76	12.747%	$181.2521	$181.25	$181.25	$181.30
Purchase #4	$38.48	7.733%	$41.4557	$41.46	$41.45	$41.50
Purchase #5	$131.55	5.315%	$138.5419	$138.54	$138.55	$138.50
Purchase #6	$132.74	6.353%	$141.173	$141.17	$141.15	$141.20
Purchase #7	$82.76	4.565%	$86.538	$86.54	$86.55	$86.50
7 purchase totals =	$645.98		$701.3273	$701.32	$701.35	$701.40