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	$109.25	6.869%	$116.7544	$116.75	$116.75	$116.80
Purchase #2	$232.28	5.681%	$245.4758	$245.48	$245.50	$245.50
Purchase #3	$135.72	13.118%	$153.5237	$153.52	$153.50	$153.50
Purchase #4	$25.73	8.175%	$27.8334	$27.83	$27.85	$27.80
Purchase #5	$21.94	13.366%	$24.8725	$24.87	$24.85	$24.90
Purchase #6	$217.89	8.206%	$235.7701	$235.77	$235.75	$235.80
Purchase #7	$102.46	8.866%	$111.5441	$111.54	$111.55	$111.50
7 purchase totals =	$845.27		$915.7740	$915.76	$915.75	$915.80