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	$43.92	8.242%	$47.5399	$47.54	$47.55	$47.50
Purchase #2	$60.74	6.375%	$64.6122	$64.61	$64.60	$64.60
Purchase #3	$73.59	11.837%	$82.3008	$82.30	$82.30	$82.30
Purchase #4	$46.73	8.839%	$50.8605	$50.86	$50.85	$50.90
Purchase #5	$138.98	4.220%	$144.845	$144.85	$144.85	$144.80
Purchase #6	$52.98	5.173%	$55.7207	$55.72	$55.70	$55.70
Purchase #7	$174.64	4.664%	$182.7852	$182.79	$182.80	$182.80
7 purchase totals =	$591.58		$628.6643	$628.67	$628.65	$628.60