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	$64.75	12.533%	$72.8651	$72.87	$72.85	$72.90
Purchase #2	$132.50	13.464%	$150.3398	$150.34	$150.35	$150.30
Purchase #3	$83.29	7.189%	$89.2777	$89.28	$89.30	$89.30
Purchase #4	$170.70	9.670%	$187.2067	$187.21	$187.20	$187.20
Purchase #5	$56.52	4.768%	$59.2149	$59.21	$59.20	$59.20
Purchase #6	$26.68	13.313%	$30.2319	$30.23	$30.25	$30.20
Purchase #7	$71.39	5.288%	$75.1651	$75.17	$75.15	$75.20
7 purchase totals =	$605.83		$664.3012	$664.31	$664.30	$664.30