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	$186.38	7.477%	$200.3156	$200.32	$200.30	$200.30
Purchase #2	$34.93	12.613%	$39.3357	$39.34	$39.35	$39.30
Purchase #3	$173.75	4.345%	$181.2994	$181.30	$181.30	$181.30
Purchase #4	$50.86	9.598%	$55.7415	$55.74	$55.75	$55.70
Purchase #5	$144.75	10.658%	$160.1775	$160.18	$160.20	$160.20
Purchase #6	$25.69	8.660%	$27.9148	$27.91	$27.90	$27.90
Purchase #7	$52.70	5.345%	$55.5168	$55.52	$55.50	$55.50
7 purchase totals =	$669.06		$720.3013	$720.31	$720.30	$720.20