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	$178.54	13.804%	$203.1857	$203.19	$203.20	$203.20
Purchase #2	$161.55	7.406%	$173.5144	$173.51	$173.50	$173.50
Purchase #3	$142.85	6.756%	$152.5009	$152.50	$152.50	$152.50
Purchase #4	$11.82	8.726%	$12.8514	$12.85	$12.85	$12.90
Purchase #5	$72.72	11.729%	$81.2493	$81.25	$81.25	$81.20
Purchase #6	$135.85	12.421%	$152.7239	$152.72	$152.70	$152.70
Purchase #7	$37.75	8.160%	$40.8304	$40.83	$40.85	$40.80
7 purchase totals =	$741.08		$816.8560	$816.85	$816.85	$816.80