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	$51.58	5.675%	$54.5072	$54.51	$54.50	$54.50
Purchase #2	$116.45	12.671%	$131.2054	$131.21	$131.20	$131.20
Purchase #3	$33.59	11.562%	$37.4737	$37.47	$37.45	$37.50
Purchase #4	$123.86	6.408%	$131.7969	$131.80	$131.80	$131.80
Purchase #5	$245.41	7.235%	$263.1654	$263.17	$263.15	$263.20
Purchase #6	$244.59	4.349%	$255.2272	$255.23	$255.25	$255.20
Purchase #7	$185.66	13.178%	$210.1263	$210.13	$210.15	$210.10
7 purchase totals =	$1,001.14		$1,083.5021	$1,083.52	$1,083.50	$1,083.50