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	$79.39	7.673%	$85.4816	$85.48	$85.50	$85.50
Purchase #2	$118.49	3.313%	$122.4156	$122.42	$122.40	$122.40
Purchase #3	$87.86	13.611%	$99.8186	$99.82	$99.80	$99.80
Purchase #4	$51.89	12.462%	$58.3565	$58.36	$58.35	$58.40
Purchase #5	$166.47	12.664%	$187.5518	$187.55	$187.55	$187.60
Purchase #6	$174.44	3.732%	$180.9501	$180.95	$180.95	$181.00
Purchase #7	$123.42	6.845%	$131.8681	$131.87	$131.85	$131.90
7 purchase totals =	$801.96		$866.4423	$866.45	$866.40	$866.60