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	$138.30	8.636%	$150.2436	$150.24	$150.25	$150.20
Purchase #2	$51.93	12.141%	$58.2348	$58.23	$58.25	$58.20
Purchase #3	$215.33	3.332%	$222.5048	$222.50	$222.50	$222.50
Purchase #4	$44.42	13.703%	$50.5069	$50.51	$50.50	$50.50
Purchase #5	$155.48	3.221%	$160.488	$160.49	$160.50	$160.50
Purchase #6	$97.81	6.566%	$104.2322	$104.23	$104.25	$104.20
Purchase #7	$211.26	8.605%	$229.4389	$229.44	$229.45	$229.40
7 purchase totals =	$914.53		$975.6492	$975.64	$975.70	$975.50