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	$134.52	4.211%	$140.1846	$140.18	$140.20	$140.20
Purchase #2	$123.78	6.499%	$131.8245	$131.82	$131.80	$131.80
Purchase #3	$131.82	9.220%	$143.9738	$143.97	$143.95	$144.00
Purchase #4	$37.58	4.264%	$39.1824	$39.18	$39.20	$39.20
Purchase #5	$184.97	3.543%	$191.5235	$191.52	$191.50	$191.50
Purchase #6	$197.61	11.541%	$220.4162	$220.42	$220.40	$220.40
Purchase #7	$104.32	12.399%	$117.2546	$117.25	$117.25	$117.30
7 purchase totals =	$914.60		$984.3596	$984.34	$984.30	$984.40