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	$7.34	10.311%	$8.0968	$8.10	$8.10	$8.10
Purchase #2	$159.86	12.198%	$179.3597	$179.36	$179.35	$179.40
Purchase #3	$82.93	7.640%	$89.2659	$89.27	$89.25	$89.30
Purchase #4	$32.61	7.179%	$34.9511	$34.95	$34.95	$35.00
Purchase #5	$102.26	11.151%	$113.663	$113.66	$113.65	$113.70
Purchase #6	$34.51	8.175%	$37.3312	$37.33	$37.35	$37.30
Purchase #7	$87.73	3.448%	$90.7549	$90.75	$90.75	$90.80
7 purchase totals =	$507.24		$553.4226	$553.42	$553.40	$553.60