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	$127.87	11.412%	$142.4625	$142.46	$142.45	$142.50
Purchase #2	$64.35	10.384%	$71.0321	$71.03	$71.05	$71.00
Purchase #3	$51.88	10.857%	$57.5126	$57.51	$57.50	$57.50
Purchase #4	$41.75	9.149%	$45.5697	$45.57	$45.55	$45.60
Purchase #5	$91.84	7.225%	$98.4754	$98.48	$98.50	$98.50
Purchase #6	$7.95	9.649%	$8.7171	$8.72	$8.70	$8.70
Purchase #7	$195.37	11.397%	$217.6363	$217.64	$217.65	$217.60
7 purchase totals =	$581.01		$641.4057	$641.41	$641.40	$641.40