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	$51.79	10.381%	$57.1663	$57.17	$57.15	$57.20
Purchase #2	$201.70	10.829%	$223.5421	$223.54	$223.55	$223.50
Purchase #3	$117.81	8.870%	$128.2597	$128.26	$128.25	$128.30
Purchase #4	$111.50	12.527%	$125.4676	$125.47	$125.45	$125.50
Purchase #5	$123.37	11.689%	$137.7907	$137.79	$137.80	$137.80
Purchase #6	$84.49	6.429%	$89.9219	$89.92	$89.90	$89.90
Purchase #7	$73.68	9.559%	$80.7231	$80.72	$80.70	$80.70
7 purchase totals =	$764.34		$842.8714	$842.87	$842.80	$842.90