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	$132.36	5.589%	$139.7576	$139.76	$139.75	$139.80
Purchase #2	$66.50	7.282%	$71.3425	$71.34	$71.35	$71.30
Purchase #3	$79.83	11.841%	$89.2827	$89.28	$89.30	$89.30
Purchase #4	$44.26	10.356%	$48.8436	$48.84	$48.85	$48.80
Purchase #5	$59.61	7.509%	$64.0861	$64.09	$64.10	$64.10
Purchase #6	$52.43	3.842%	$54.4444	$54.44	$54.45	$54.40
Purchase #7	$83.85	13.641%	$95.288	$95.29	$95.30	$95.30
7 purchase totals =	$518.84		$563.0449	$563.04	$563.10	$563.00