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	$69.98	11.474%	$78.0095	$78.01	$78.00	$78.00
Purchase #2	$144.62	3.865%	$150.2096	$150.21	$150.20	$150.20
Purchase #3	$10.66	11.272%	$11.8616	$11.86	$11.85	$11.90
Purchase #4	$49.87	9.330%	$54.5229	$54.52	$54.50	$54.50
Purchase #5	$80.44	11.312%	$89.5394	$89.54	$89.55	$89.50
Purchase #6	$74.63	11.714%	$83.3722	$83.37	$83.35	$83.40
Purchase #7	$73.81	8.433%	$80.0344	$80.03	$80.05	$80.00
7 purchase totals =	$504.01		$547.5496	$547.54	$547.50	$547.50