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	$229.44	13.435%	$260.2653	$260.27	$260.25	$260.30
Purchase #2	$200.30	5.161%	$210.6375	$210.64	$210.65	$210.60
Purchase #3	$79.35	4.463%	$82.8914	$82.89	$82.90	$82.90
Purchase #4	$28.77	10.406%	$31.7638	$31.76	$31.75	$31.80
Purchase #5	$138.57	7.170%	$148.5055	$148.51	$148.50	$148.50
Purchase #6	$59.59	7.217%	$63.8906	$63.89	$63.90	$63.90
Purchase #7	$193.89	5.749%	$205.0367	$205.04	$205.05	$205.00
7 purchase totals =	$929.91		$1,002.9908	$1,003.00	$1,003.00	$1,003.00