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	$196.98	11.648%	$219.9242	$219.92	$219.90	$219.90
Purchase #2	$45.61	9.652%	$50.0123	$50.01	$50.00	$50.00
Purchase #3	$112.48	11.768%	$125.7166	$125.72	$125.70	$125.70
Purchase #4	$102.90	6.735%	$109.8303	$109.83	$109.85	$109.80
Purchase #5	$51.42	3.761%	$53.3539	$53.35	$53.35	$53.40
Purchase #6	$184.56	4.406%	$192.6917	$192.69	$192.70	$192.70
Purchase #7	$83.64	8.661%	$90.8841	$90.88	$90.90	$90.90
7 purchase totals =	$777.59		$842.4131	$842.40	$842.40	$842.40