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	$128.90	6.734%	$137.5801	$137.58	$137.60	$137.60
Purchase #2	$161.54	6.387%	$171.8576	$171.86	$171.85	$171.90
Purchase #3	$96.77	10.716%	$107.1399	$107.14	$107.15	$107.10
Purchase #4	$41.69	3.197%	$43.0228	$43.02	$43.00	$43.00
Purchase #5	$227.32	11.522%	$253.5118	$253.51	$253.50	$253.50
Purchase #6	$243.65	12.256%	$273.5117	$273.51	$273.50	$273.50
Purchase #7	$136.72	10.212%	$150.6818	$150.68	$150.70	$150.70
7 purchase totals =	$1,036.59		$1,137.3057	$1,137.30	$1,137.30	$1,137.30