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	$117.84	3.112%	$121.5072	$121.51	$121.50	$121.50
Purchase #2	$68.48	4.536%	$71.5863	$71.59	$71.60	$71.60
Purchase #3	$120.42	9.842%	$132.2717	$132.27	$132.25	$132.30
Purchase #4	$220.93	4.802%	$231.5391	$231.54	$231.55	$231.50
Purchase #5	$50.29	6.742%	$53.6806	$53.68	$53.70	$53.70
Purchase #6	$100.57	8.466%	$109.0843	$109.08	$109.10	$109.10
Purchase #7	$96.36	3.174%	$99.4185	$99.42	$99.40	$99.40
7 purchase totals =	$774.89		$819.0877	$819.09	$819.10	$819.10