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	$241.85	11.287%	$269.1476	$269.15	$269.15	$269.10
Purchase #2	$62.85	7.722%	$67.7033	$67.70	$67.70	$67.70
Purchase #3	$100.50	5.456%	$105.9833	$105.98	$106.00	$106.00
Purchase #4	$29.35	6.751%	$31.3314	$31.33	$31.35	$31.30
Purchase #5	$99.31	10.831%	$110.0663	$110.07	$110.05	$110.10
Purchase #6	$134.81	5.737%	$142.544	$142.54	$142.55	$142.50
Purchase #7	$44.90	11.708%	$50.1569	$50.16	$50.15	$50.20
7 purchase totals =	$713.57		$776.9328	$776.93	$776.95	$776.90