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	$90.42	11.539%	$100.8536	$100.85	$100.85	$100.90
Purchase #2	$225.95	10.365%	$249.3697	$249.37	$249.35	$249.40
Purchase #3	$214.61	5.555%	$226.5316	$226.53	$226.55	$226.50
Purchase #4	$125.57	3.245%	$129.6447	$129.64	$129.65	$129.60
Purchase #5	$25.88	10.583%	$28.6189	$28.62	$28.60	$28.60
Purchase #6	$237.84	8.695%	$258.5202	$258.52	$258.50	$258.50
Purchase #7	$52.51	5.672%	$55.4884	$55.49	$55.50	$55.50
7 purchase totals =	$972.78		$1,049.0271	$1,049.02	$1,049.00	$1,049.00