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	$203.77	10.860%	$225.8994	$225.90	$225.90	$225.90
Purchase #2	$203.48	8.794%	$221.374	$221.37	$221.35	$221.40
Purchase #3	$59.41	5.780%	$62.8439	$62.84	$62.85	$62.80
Purchase #4	$133.78	3.800%	$138.8636	$138.86	$138.85	$138.90
Purchase #5	$170.63	3.247%	$176.1704	$176.17	$176.15	$176.20
Purchase #6	$57.47	3.210%	$59.3148	$59.31	$59.30	$59.30
Purchase #7	$80.71	11.776%	$90.2144	$90.21	$90.20	$90.20
7 purchase totals =	$909.25		$974.6805	$974.66	$974.60	$974.70