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	$74.80	8.157%	$80.9014	$80.90	$80.90	$80.90
Purchase #2	$149.82	3.812%	$155.5311	$155.53	$155.55	$155.50
Purchase #3	$123.47	12.793%	$139.2655	$139.27	$139.25	$139.30
Purchase #4	$51.88	13.870%	$59.0758	$59.08	$59.10	$59.10
Purchase #5	$234.58	9.320%	$256.4429	$256.44	$256.45	$256.40
Purchase #6	$79.82	9.636%	$87.5115	$87.51	$87.50	$87.50
Purchase #7	$44.33	12.437%	$49.8433	$49.84	$49.85	$49.80
7 purchase totals =	$758.70		$828.5715	$828.57	$828.60	$828.50