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	$240.28	12.386%	$270.0411	$270.04	$270.05	$270.00
Purchase #2	$139.50	10.759%	$154.5088	$154.51	$154.50	$154.50
Purchase #3	$32.60	10.110%	$35.8959	$35.90	$35.90	$35.90
Purchase #4	$121.96	7.862%	$131.5485	$131.55	$131.55	$131.50
Purchase #5	$203.79	9.215%	$222.5692	$222.57	$222.55	$222.60
Purchase #6	$96.55	11.332%	$107.491	$107.49	$107.50	$107.50
Purchase #7	$136.64	6.585%	$145.6377	$145.64	$145.65	$145.60
7 purchase totals =	$971.32		$1,067.6922	$1,067.70	$1,067.70	$1,067.60