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	$131.89	8.342%	$142.8923	$142.89	$142.90	$142.90
Purchase #2	$113.79	9.212%	$124.2723	$124.27	$124.25	$124.30
Purchase #3	$133.82	10.492%	$147.8604	$147.86	$147.85	$147.90
Purchase #4	$85.99	5.525%	$90.7409	$90.74	$90.75	$90.70
Purchase #5	$133.57	8.580%	$145.0303	$145.03	$145.05	$145.00
Purchase #6	$155.52	12.434%	$174.8574	$174.86	$174.85	$174.90
Purchase #7	$73.97	3.816%	$76.7927	$76.79	$76.80	$76.80
7 purchase totals =	$828.55		$902.4463	$902.44	$902.45	$902.50