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	$63.44	12.209%	$71.1854	$71.19	$71.20	$71.20
Purchase #2	$25.81	12.731%	$29.0959	$29.10	$29.10	$29.10
Purchase #3	$82.57	8.828%	$89.8593	$89.86	$89.85	$89.90
Purchase #4	$111.48	8.259%	$120.6871	$120.69	$120.70	$120.70
Purchase #5	$16.35	11.616%	$18.2492	$18.25	$18.25	$18.20
Purchase #6	$164.37	10.416%	$181.4908	$181.49	$181.50	$181.50
Purchase #7	$39.88	5.538%	$42.0886	$42.09	$42.10	$42.10
7 purchase totals =	$503.90		$552.6563	$552.67	$552.70	$552.70