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	$121.56	12.276%	$136.4827	$136.48	$136.50	$136.50
Purchase #2	$117.76	5.222%	$123.9094	$123.91	$123.90	$123.90
Purchase #3	$172.91	7.104%	$185.1935	$185.19	$185.20	$185.20
Purchase #4	$85.92	5.196%	$90.3844	$90.38	$90.40	$90.40
Purchase #5	$14.56	12.742%	$16.4152	$16.42	$16.40	$16.40
Purchase #6	$116.67	3.733%	$121.0253	$121.03	$121.05	$121.00
Purchase #7	$131.94	3.488%	$136.5421	$136.54	$136.55	$136.50
7 purchase totals =	$761.32		$809.9526	$809.95	$810.00	$809.90