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	$123.90	8.859%	$134.8763	$134.88	$134.90	$134.90
Purchase #2	$37.52	13.198%	$42.4719	$42.47	$42.45	$42.50
Purchase #3	$232.87	3.597%	$241.2463	$241.25	$241.25	$241.20
Purchase #4	$229.55	6.498%	$244.4662	$244.47	$244.45	$244.50
Purchase #5	$56.29	8.708%	$61.1917	$61.19	$61.20	$61.20
Purchase #6	$148.70	6.299%	$158.0666	$158.07	$158.05	$158.10
Purchase #7	$219.29	13.751%	$249.4446	$249.44	$249.45	$249.40
7 purchase totals =	$1,048.12		$1,131.7636	$1,131.77	$1,131.75	$1,131.80