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	$109.37	13.349%	$123.9698	$123.97	$123.95	$124.00
Purchase #2	$161.58	7.198%	$173.2105	$173.21	$173.20	$173.20
Purchase #3	$96.34	13.296%	$109.1494	$109.15	$109.15	$109.10
Purchase #4	$107.46	10.192%	$118.4123	$118.41	$118.40	$118.40
Purchase #5	$54.84	13.751%	$62.381	$62.38	$62.40	$62.40
Purchase #6	$37.81	9.207%	$41.2912	$41.29	$41.30	$41.30
Purchase #7	$150.78	7.792%	$162.5288	$162.53	$162.55	$162.50
7 purchase totals =	$718.18		$790.9430	$790.94	$790.95	$790.90