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	$39.47	10.261%	$43.52	$43.52	$43.50	$43.50
Purchase #2	$250.30	12.140%	$280.6864	$280.69	$280.70	$280.70
Purchase #3	$140.71	7.661%	$151.4898	$151.49	$151.50	$151.50
Purchase #4	$30.58	4.794%	$32.046	$32.05	$32.05	$32.00
Purchase #5	$179.26	11.829%	$200.4647	$200.46	$200.45	$200.50
Purchase #6	$82.30	3.860%	$85.4768	$85.48	$85.50	$85.50
Purchase #7	$249.60	12.844%	$281.6586	$281.66	$281.65	$281.70
7 purchase totals =	$972.22		$1,075.3423	$1,075.35	$1,075.35	$1,075.40