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	$153.75	8.404%	$166.6712	$166.67	$166.65	$166.70
Purchase #2	$119.38	9.409%	$130.6125	$130.61	$130.60	$130.60
Purchase #3	$109.86	13.583%	$124.7823	$124.78	$124.80	$124.80
Purchase #4	$212.50	5.145%	$223.4331	$223.43	$223.45	$223.40
Purchase #5	$197.40	11.748%	$220.5906	$220.59	$220.60	$220.60
Purchase #6	$41.39	8.746%	$45.01	$45.01	$45.00	$45.00
Purchase #7	$225.57	6.652%	$240.5749	$240.57	$240.55	$240.60
7 purchase totals =	$1,059.85		$1,151.6746	$1,151.66	$1,151.65	$1,151.70