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	$6.55	11.201%	$7.2837	$7.28	$7.30	$7.30
Purchase #2	$129.35	11.152%	$143.7751	$143.78	$143.80	$143.80
Purchase #3	$213.79	8.349%	$231.6393	$231.64	$231.65	$231.60
Purchase #4	$82.72	9.565%	$90.6322	$90.63	$90.65	$90.60
Purchase #5	$108.59	13.505%	$123.2551	$123.26	$123.25	$123.30
Purchase #6	$41.92	8.447%	$45.461	$45.46	$45.45	$45.50
Purchase #7	$173.93	12.188%	$195.1286	$195.13	$195.15	$195.10
7 purchase totals =	$756.85		$837.1750	$837.18	$837.25	$837.20