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	$55.40	13.681%	$62.9793	$62.98	$63.00	$63.00
Purchase #2	$244.72	9.684%	$268.4187	$268.42	$268.40	$268.40
Purchase #3	$180.80	12.705%	$203.7706	$203.77	$203.75	$203.80
Purchase #4	$16.66	9.675%	$18.2719	$18.27	$18.25	$18.30
Purchase #5	$209.59	11.509%	$233.7117	$233.71	$233.70	$233.70
Purchase #6	$124.51	5.415%	$131.2522	$131.25	$131.25	$131.30
Purchase #7	$173.27	3.534%	$179.3934	$179.39	$179.40	$179.40
7 purchase totals =	$1,004.95		$1,097.7978	$1,097.79	$1,097.75	$1,097.90