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	$108.63	8.163%	$117.4975	$117.50	$117.50	$117.50
Purchase #2	$210.35	9.241%	$229.7884	$229.79	$229.80	$229.80
Purchase #3	$193.71	5.116%	$203.6202	$203.62	$203.60	$203.60
Purchase #4	$109.85	12.411%	$123.4835	$123.48	$123.50	$123.50
Purchase #5	$161.48	9.314%	$176.5202	$176.52	$176.50	$176.50
Purchase #6	$187.33	10.125%	$206.2972	$206.30	$206.30	$206.30
Purchase #7	$40.46	7.823%	$43.6252	$43.63	$43.65	$43.60
7 purchase totals =	$1,011.81		$1,100.8322	$1,100.84	$1,100.85	$1,100.80