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	$104.91	6.315%	$111.5351	$111.54	$111.55	$111.50
Purchase #2	$123.25	10.439%	$136.1161	$136.12	$136.10	$136.10
Purchase #3	$241.26	13.480%	$273.7818	$273.78	$273.80	$273.80
Purchase #4	$148.88	9.298%	$162.7229	$162.72	$162.70	$162.70
Purchase #5	$81.85	6.798%	$87.4142	$87.41	$87.40	$87.40
Purchase #6	$184.34	7.587%	$198.3259	$198.33	$198.35	$198.30
Purchase #7	$123.96	10.754%	$137.2907	$137.29	$137.30	$137.30
7 purchase totals =	$1,008.45		$1,107.1867	$1,107.19	$1,107.20	$1,107.10