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	$250.54	3.283%	$258.7652	$258.77	$258.75	$258.80
Purchase #2	$140.27	13.456%	$159.1447	$159.14	$159.15	$159.10
Purchase #3	$81.60	3.785%	$84.6886	$84.69	$84.70	$84.70
Purchase #4	$78.56	13.634%	$89.2709	$89.27	$89.25	$89.30
Purchase #5	$144.34	13.810%	$164.2734	$164.27	$164.25	$164.30
Purchase #6	$195.71	9.479%	$214.2614	$214.26	$214.25	$214.30
Purchase #7	$129.77	10.611%	$143.5399	$143.54	$143.55	$143.50
7 purchase totals =	$1,020.79		$1,113.9441	$1,113.94	$1,113.90	$1,114.00