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	$204.86	12.833%	$231.1497	$231.15	$231.15	$231.10
Purchase #2	$110.70	11.357%	$123.2722	$123.27	$123.25	$123.30
Purchase #3	$163.38	7.153%	$175.0666	$175.07	$175.05	$175.10
Purchase #4	$73.69	6.779%	$78.6854	$78.69	$78.70	$78.70
Purchase #5	$55.45	11.778%	$61.9809	$61.98	$62.00	$62.00
Purchase #6	$217.32	10.849%	$240.897	$240.90	$240.90	$240.90
Purchase #7	$53.63	6.386%	$57.0548	$57.05	$57.05	$57.10
7 purchase totals =	$879.03		$968.1066	$968.11	$968.10	$968.20