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	$161.54	6.836%	$172.5829	$172.58	$172.60	$172.60
Purchase #2	$123.43	9.264%	$134.8646	$134.86	$134.85	$134.90
Purchase #3	$32.87	12.585%	$37.0067	$37.01	$37.00	$37.00
Purchase #4	$45.76	6.398%	$48.6877	$48.69	$48.70	$48.70
Purchase #5	$50.70	9.168%	$55.3482	$55.35	$55.35	$55.30
Purchase #6	$123.96	3.826%	$128.7027	$128.70	$128.70	$128.70
Purchase #7	$223.59	11.106%	$248.4219	$248.42	$248.40	$248.40
7 purchase totals =	$761.85		$825.6147	$825.61	$825.60	$825.60