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	$136.84	11.674%	$152.8147	$152.81	$152.80	$152.80
Purchase #2	$166.32	12.394%	$186.9337	$186.93	$186.95	$186.90
Purchase #3	$53.96	9.755%	$59.2238	$59.22	$59.20	$59.20
Purchase #4	$233.51	9.510%	$255.7168	$255.72	$255.70	$255.70
Purchase #5	$124.65	12.153%	$139.7987	$139.80	$139.80	$139.80
Purchase #6	$30.52	11.190%	$33.9352	$33.94	$33.95	$33.90
Purchase #7	$171.55	5.681%	$181.2958	$181.30	$181.30	$181.30
7 purchase totals =	$917.35		$1,009.7187	$1,009.72	$1,009.70	$1,009.60