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	$113.48	12.498%	$127.6627	$127.66	$127.65	$127.70
Purchase #2	$150.53	3.479%	$155.7669	$155.77	$155.75	$155.80
Purchase #3	$39.53	7.599%	$42.5339	$42.53	$42.55	$42.50
Purchase #4	$145.88	3.677%	$151.244	$151.24	$151.25	$151.20
Purchase #5	$81.44	9.856%	$89.4667	$89.47	$89.45	$89.50
Purchase #6	$93.79	12.377%	$105.3984	$105.40	$105.40	$105.40
Purchase #7	$171.58	5.161%	$180.4352	$180.44	$180.45	$180.40
7 purchase totals =	$796.23		$852.5078	$852.51	$852.50	$852.50