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	$226.60	7.135%	$242.7679	$242.77	$242.75	$242.80
Purchase #2	$216.42	12.554%	$243.5894	$243.59	$243.60	$243.60
Purchase #3	$119.44	7.773%	$128.7241	$128.72	$128.70	$128.70
Purchase #4	$93.65	11.520%	$104.4385	$104.44	$104.45	$104.40
Purchase #5	$210.72	4.130%	$219.4227	$219.42	$219.40	$219.40
Purchase #6	$186.90	7.329%	$200.5979	$200.60	$200.60	$200.60
Purchase #7	$28.82	10.428%	$31.8253	$31.83	$31.85	$31.80
7 purchase totals =	$1,082.55		$1,171.3658	$1,171.37	$1,171.35	$1,171.30