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	$30.31	4.123%	$31.5597	$31.56	$31.55	$31.60
Purchase #2	$78.45	8.611%	$85.2053	$85.21	$85.20	$85.20
Purchase #3	$104.94	9.613%	$115.0279	$115.03	$115.05	$115.00
Purchase #4	$81.31	7.382%	$87.3123	$87.31	$87.30	$87.30
Purchase #5	$66.76	11.538%	$74.4628	$74.46	$74.45	$74.50
Purchase #6	$52.38	8.601%	$56.8852	$56.89	$56.90	$56.90
Purchase #7	$127.79	9.421%	$139.8291	$139.83	$139.85	$139.80
7 purchase totals =	$541.94		$590.2823	$590.29	$590.30	$590.30