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	$9.60	8.782%	$10.4431	$10.44	$10.45	$10.40
Purchase #2	$228.50	4.368%	$238.4809	$238.48	$238.50	$238.50
Purchase #3	$219.40	5.299%	$231.026	$231.03	$231.05	$231.00
Purchase #4	$57.64	7.299%	$61.8471	$61.85	$61.85	$61.80
Purchase #5	$124.86	10.453%	$137.9116	$137.91	$137.90	$137.90
Purchase #6	$129.59	3.332%	$133.9079	$133.91	$133.90	$133.90
Purchase #7	$100.38	3.470%	$103.8632	$103.86	$103.85	$103.90
7 purchase totals =	$869.97		$917.4798	$917.48	$917.50	$917.40