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	$52.38	3.342%	$54.1305	$54.13	$54.15	$54.10
Purchase #2	$170.80	12.136%	$191.5283	$191.53	$191.55	$191.50
Purchase #3	$202.86	9.768%	$222.6754	$222.68	$222.70	$222.70
Purchase #4	$75.88	3.584%	$78.5995	$78.60	$78.60	$78.60
Purchase #5	$160.89	4.521%	$168.1638	$168.16	$168.15	$168.20
Purchase #6	$117.34	10.185%	$129.2911	$129.29	$129.30	$129.30
Purchase #7	$25.47	6.797%	$27.2012	$27.20	$27.20	$27.20
7 purchase totals =	$805.62		$871.5898	$871.59	$871.65	$871.60