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	$203.90	6.105%	$216.3481	$216.35	$216.35	$216.30
Purchase #2	$193.33	3.593%	$200.2763	$200.28	$200.30	$200.30
Purchase #3	$38.46	13.838%	$43.7821	$43.78	$43.80	$43.80
Purchase #4	$29.71	7.739%	$32.0093	$32.01	$32.00	$32.00
Purchase #5	$55.68	13.746%	$63.3338	$63.33	$63.35	$63.30
Purchase #6	$56.81	10.282%	$62.6512	$62.65	$62.65	$62.70
Purchase #7	$47.57	11.178%	$52.8874	$52.89	$52.90	$52.90
7 purchase totals =	$625.46		$671.2882	$671.29	$671.35	$671.30