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	$250.86	11.178%	$278.9011	$278.90	$278.90	$278.90
Purchase #2	$157.57	7.633%	$169.5973	$169.60	$169.60	$169.60
Purchase #3	$51.92	8.438%	$56.301	$56.30	$56.30	$56.30
Purchase #4	$163.46	11.617%	$182.4491	$182.45	$182.45	$182.40
Purchase #5	$94.32	6.801%	$100.7347	$100.73	$100.75	$100.70
Purchase #6	$147.53	11.300%	$164.2009	$164.20	$164.20	$164.20
Purchase #7	$108.82	7.842%	$117.3537	$117.35	$117.35	$117.40
7 purchase totals =	$974.48		$1,069.5378	$1,069.53	$1,069.55	$1,069.50