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	$62.54	6.710%	$66.7364	$66.74	$66.75	$66.70
Purchase #2	$31.91	4.740%	$33.4225	$33.42	$33.40	$33.40
Purchase #3	$99.96	4.245%	$104.2033	$104.20	$104.20	$104.20
Purchase #4	$77.34	10.538%	$85.4901	$85.49	$85.50	$85.50
Purchase #5	$124.62	11.458%	$138.899	$138.90	$138.90	$138.90
Purchase #6	$246.46	6.464%	$262.3912	$262.39	$262.40	$262.40
Purchase #7	$95.98	4.477%	$100.277	$100.28	$100.30	$100.30
7 purchase totals =	$738.81		$791.4195	$791.42	$791.45	$791.40