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	$126.96	9.797%	$139.3983	$139.40	$139.40	$139.40
Purchase #2	$153.42	5.682%	$162.1373	$162.14	$162.15	$162.10
Purchase #3	$250.84	9.549%	$274.7927	$274.79	$274.80	$274.80
Purchase #4	$27.33	13.699%	$31.0739	$31.07	$31.05	$31.10
Purchase #5	$69.89	12.105%	$78.3502	$78.35	$78.35	$78.40
Purchase #6	$202.36	6.584%	$215.6834	$215.68	$215.70	$215.70
Purchase #7	$182.96	3.825%	$189.9582	$189.96	$189.95	$190.00
7 purchase totals =	$1,013.76		$1,091.3940	$1,091.39	$1,091.40	$1,091.50