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	$129.73	5.561%	$136.9443	$136.94	$136.95	$136.90
Purchase #2	$165.36	8.454%	$179.3395	$179.34	$179.35	$179.30
Purchase #3	$80.33	13.214%	$90.9448	$90.94	$90.95	$90.90
Purchase #4	$109.41	3.248%	$112.9636	$112.96	$112.95	$113.00
Purchase #5	$144.71	4.233%	$150.8356	$150.84	$150.85	$150.80
Purchase #6	$149.49	4.779%	$156.6341	$156.63	$156.65	$156.60
Purchase #7	$55.37	4.449%	$57.8334	$57.83	$57.85	$57.80
7 purchase totals =	$834.40		$885.4953	$885.48	$885.55	$885.30