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	$248.53	12.586%	$279.81	$279.81	$279.80	$279.80
Purchase #2	$199.59	10.467%	$220.4811	$220.48	$220.50	$220.50
Purchase #3	$129.60	8.506%	$140.6238	$140.62	$140.60	$140.60
Purchase #4	$175.46	9.243%	$191.6778	$191.68	$191.70	$191.70
Purchase #5	$70.83	10.223%	$78.071	$78.07	$78.05	$78.10
Purchase #6	$5.68	10.715%	$6.2886	$6.29	$6.30	$6.30
Purchase #7	$161.63	6.582%	$172.2685	$172.27	$172.25	$172.30
7 purchase totals =	$991.32		$1,089.2208	$1,089.22	$1,089.20	$1,089.30