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	$237.52	13.704%	$270.0697	$270.07	$270.05	$270.10
Purchase #2	$62.84	7.363%	$67.4669	$67.47	$67.45	$67.50
Purchase #3	$181.70	8.250%	$196.6903	$196.69	$196.70	$196.70
Purchase #4	$90.88	10.814%	$100.7078	$100.71	$100.70	$100.70
Purchase #5	$112.35	6.691%	$119.8673	$119.87	$119.85	$119.90
Purchase #6	$80.87	5.159%	$85.0421	$85.04	$85.05	$85.00
Purchase #7	$88.44	9.166%	$96.5464	$96.55	$96.55	$96.50
7 purchase totals =	$854.60		$936.3905	$936.40	$936.35	$936.40