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	$228.37	12.364%	$256.6057	$256.61	$256.60	$256.60
Purchase #2	$52.57	12.658%	$59.2243	$59.22	$59.20	$59.20
Purchase #3	$8.50	8.464%	$9.2194	$9.22	$9.20	$9.20
Purchase #4	$92.53	12.281%	$103.8936	$103.89	$103.90	$103.90
Purchase #5	$164.25	4.493%	$171.6298	$171.63	$171.65	$171.60
Purchase #6	$149.56	11.471%	$166.716	$166.72	$166.70	$166.70
Purchase #7	$201.80	12.703%	$227.4347	$227.43	$227.45	$227.40
7 purchase totals =	$897.58		$994.7235	$994.72	$994.70	$994.60