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	$130.28	11.681%	$145.498	$145.50	$145.50	$145.50
Purchase #2	$212.47	6.493%	$226.2657	$226.27	$226.25	$226.30
Purchase #3	$103.92	6.374%	$110.5439	$110.54	$110.55	$110.50
Purchase #4	$161.72	4.455%	$168.9246	$168.92	$168.90	$168.90
Purchase #5	$205.54	9.840%	$225.7651	$225.77	$225.75	$225.80
Purchase #6	$56.67	10.822%	$62.8028	$62.80	$62.80	$62.80
Purchase #7	$38.50	4.225%	$40.1266	$40.13	$40.15	$40.10
7 purchase totals =	$909.10		$979.9267	$979.93	$979.90	$979.90