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	$170.85	13.641%	$194.1556	$194.16	$194.15	$194.20
Purchase #2	$117.25	5.539%	$123.7445	$123.74	$123.75	$123.70
Purchase #3	$232.32	10.535%	$256.7949	$256.79	$256.80	$256.80
Purchase #4	$178.27	5.741%	$188.5045	$188.50	$188.50	$188.50
Purchase #5	$78.82	10.314%	$86.9495	$86.95	$86.95	$86.90
Purchase #6	$86.42	4.511%	$90.3184	$90.32	$90.30	$90.30
Purchase #7	$33.86	13.357%	$38.3827	$38.38	$38.40	$38.40
7 purchase totals =	$897.79		$978.8501	$978.84	$978.85	$978.80