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	$143.60	3.325%	$148.3747	$148.37	$148.35	$148.40
Purchase #2	$123.72	6.478%	$131.7346	$131.73	$131.75	$131.70
Purchase #3	$118.84	4.780%	$124.5206	$124.52	$124.50	$124.50
Purchase #4	$39.42	9.652%	$43.2248	$43.22	$43.20	$43.20
Purchase #5	$174.91	8.574%	$189.9068	$189.91	$189.90	$189.90
Purchase #6	$223.27	12.266%	$250.6563	$250.66	$250.65	$250.70
Purchase #7	$134.65	11.722%	$150.4337	$150.43	$150.45	$150.40
7 purchase totals =	$958.41		$1,038.8515	$1,038.84	$1,038.80	$1,038.80