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	$99.27	10.197%	$109.3926	$109.39	$109.40	$109.40
Purchase #2	$172.64	8.654%	$187.5803	$187.58	$187.60	$187.60
Purchase #3	$99.28	12.864%	$112.0514	$112.05	$112.05	$112.10
Purchase #4	$236.77	5.185%	$249.0465	$249.05	$249.05	$249.00
Purchase #5	$113.88	3.457%	$117.8168	$117.82	$117.80	$117.80
Purchase #6	$41.42	9.592%	$45.393	$45.39	$45.40	$45.40
Purchase #7	$245.99	5.714%	$260.0459	$260.05	$260.05	$260.00
7 purchase totals =	$1,009.25		$1,081.3265	$1,081.33	$1,081.35	$1,081.30