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	$25.82	6.547%	$27.5104	$27.51	$27.50	$27.50
Purchase #2	$156.35	9.817%	$171.6989	$171.70	$171.70	$171.70
Purchase #3	$200.54	6.501%	$213.5771	$213.58	$213.60	$213.60
Purchase #4	$238.77	13.315%	$270.5622	$270.56	$270.55	$270.60
Purchase #5	$103.85	7.780%	$111.9295	$111.93	$111.95	$111.90
Purchase #6	$129.87	12.248%	$145.7765	$145.78	$145.80	$145.80
Purchase #7	$110.55	8.314%	$119.7411	$119.74	$119.75	$119.70
7 purchase totals =	$965.75		$1,060.7957	$1,060.80	$1,060.85	$1,060.80