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	$159.92	12.670%	$180.1819	$180.18	$180.20	$180.20
Purchase #2	$131.30	7.583%	$141.2565	$141.26	$141.25	$141.30
Purchase #3	$79.35	13.652%	$90.1829	$90.18	$90.20	$90.20
Purchase #4	$102.73	5.388%	$108.2651	$108.27	$108.25	$108.30
Purchase #5	$89.75	6.845%	$95.8934	$95.89	$95.90	$95.90
Purchase #6	$10.33	11.247%	$11.4918	$11.49	$11.50	$11.50
Purchase #7	$128.25	12.331%	$144.0645	$144.06	$144.05	$144.10
7 purchase totals =	$701.63		$771.3361	$771.33	$771.35	$771.50