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	$155.48	12.476%	$174.8777	$174.88	$174.90	$174.90
Purchase #2	$47.89	4.647%	$50.1154	$50.12	$50.10	$50.10
Purchase #3	$113.46	4.504%	$118.5702	$118.57	$118.55	$118.60
Purchase #4	$151.66	3.317%	$156.6906	$156.69	$156.70	$156.70
Purchase #5	$82.85	9.546%	$90.7589	$90.76	$90.75	$90.80
Purchase #6	$29.87	4.708%	$31.2763	$31.28	$31.30	$31.30
Purchase #7	$17.52	12.785%	$19.7599	$19.76	$19.75	$19.80
7 purchase totals =	$598.73		$642.0490	$642.06	$642.05	$642.20