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	$113.74	3.326%	$117.523	$117.52	$117.50	$117.50
Purchase #2	$139.47	7.586%	$150.0502	$150.05	$150.05	$150.10
Purchase #3	$44.73	6.413%	$47.5985	$47.60	$47.60	$47.60
Purchase #4	$119.82	10.705%	$132.6467	$132.65	$132.65	$132.60
Purchase #5	$199.88	8.138%	$216.1462	$216.15	$216.15	$216.10
Purchase #6	$119.91	9.625%	$131.4513	$131.45	$131.45	$131.50
Purchase #7	$250.34	13.210%	$283.4099	$283.41	$283.40	$283.40
7 purchase totals =	$987.89		$1,078.8258	$1,078.83	$1,078.80	$1,078.80