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	$53.64	12.485%	$60.337	$60.34	$60.35	$60.30
Purchase #2	$114.39	7.814%	$123.3284	$123.33	$123.35	$123.30
Purchase #3	$25.65	13.221%	$29.0412	$29.04	$29.05	$29.00
Purchase #4	$110.25	11.653%	$123.0974	$123.10	$123.10	$123.10
Purchase #5	$56.39	5.861%	$59.695	$59.70	$59.70	$59.70
Purchase #6	$34.79	4.689%	$36.4213	$36.42	$36.40	$36.40
Purchase #7	$196.31	10.543%	$217.007	$217.01	$217.00	$217.00
7 purchase totals =	$591.42		$648.9273	$648.94	$648.95	$648.80