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	$99.37	6.543%	$105.8718	$105.87	$105.85	$105.90
Purchase #2	$116.64	10.718%	$129.1415	$129.14	$129.15	$129.10
Purchase #3	$145.95	6.317%	$155.1697	$155.17	$155.15	$155.20
Purchase #4	$86.75	8.853%	$94.43	$94.43	$94.45	$94.40
Purchase #5	$85.49	5.782%	$90.433	$90.43	$90.45	$90.40
Purchase #6	$89.57	7.630%	$96.4042	$96.40	$96.40	$96.40
Purchase #7	$225.73	8.624%	$245.197	$245.20	$245.20	$245.20
7 purchase totals =	$849.50		$916.6472	$916.64	$916.65	$916.60