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	$50.62	10.116%	$55.7407	$55.74	$55.75	$55.70
Purchase #2	$125.90	12.623%	$141.7924	$141.79	$141.80	$141.80
Purchase #3	$81.33	11.164%	$90.4097	$90.41	$90.40	$90.40
Purchase #4	$199.79	9.706%	$219.1816	$219.18	$219.20	$219.20
Purchase #5	$116.45	9.357%	$127.3462	$127.35	$127.35	$127.30
Purchase #6	$137.51	13.311%	$155.814	$155.81	$155.80	$155.80
Purchase #7	$224.78	11.259%	$250.088	$250.09	$250.10	$250.10
7 purchase totals =	$936.38		$1,040.3726	$1,040.37	$1,040.40	$1,040.30