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	$249.63	11.431%	$278.1652	$278.17	$278.15	$278.20
Purchase #2	$84.87	6.214%	$90.1438	$90.14	$90.15	$90.10
Purchase #3	$217.80	3.392%	$225.1878	$225.19	$225.20	$225.20
Purchase #4	$168.45	5.219%	$177.2414	$177.24	$177.25	$177.20
Purchase #5	$63.52	6.638%	$67.7365	$67.74	$67.75	$67.70
Purchase #6	$149.46	10.752%	$165.5299	$165.53	$165.55	$165.50
Purchase #7	$52.28	9.675%	$57.3381	$57.34	$57.35	$57.30
7 purchase totals =	$986.01		$1,061.3427	$1,061.35	$1,061.40	$1,061.20