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	$54.57	8.269%	$59.0824	$59.08	$59.10	$59.10
Purchase #2	$136.82	4.185%	$142.5459	$142.55	$142.55	$142.50
Purchase #3	$55.96	12.352%	$62.8722	$62.87	$62.85	$62.90
Purchase #4	$250.90	8.868%	$273.1498	$273.15	$273.15	$273.10
Purchase #5	$28.69	13.859%	$32.6661	$32.67	$32.65	$32.70
Purchase #6	$60.57	10.140%	$66.7118	$66.71	$66.70	$66.70
Purchase #7	$180.98	13.704%	$205.7815	$205.78	$205.80	$205.80
7 purchase totals =	$768.49		$842.8097	$842.81	$842.80	$842.80