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	$138.27	9.714%	$151.7015	$151.70	$151.70	$151.70
Purchase #2	$148.41	5.770%	$156.9733	$156.97	$156.95	$157.00
Purchase #3	$90.34	12.246%	$101.403	$101.40	$101.40	$101.40
Purchase #4	$66.88	7.535%	$71.9194	$71.92	$71.90	$71.90
Purchase #5	$128.40	9.206%	$140.2205	$140.22	$140.20	$140.20
Purchase #6	$182.25	10.225%	$200.8851	$200.89	$200.90	$200.90
Purchase #7	$246.60	4.362%	$257.3567	$257.36	$257.35	$257.40
7 purchase totals =	$1,001.15		$1,080.4595	$1,080.46	$1,080.40	$1,080.50