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	$140.62	13.120%	$159.0693	$159.07	$159.05	$159.10
Purchase #2	$249.47	12.284%	$280.1149	$280.11	$280.10	$280.10
Purchase #3	$125.39	13.676%	$142.5383	$142.54	$142.55	$142.50
Purchase #4	$140.59	5.505%	$148.3295	$148.33	$148.35	$148.30
Purchase #5	$75.50	10.702%	$83.58	$83.58	$83.60	$83.60
Purchase #6	$172.92	4.718%	$181.0784	$181.08	$181.10	$181.10
Purchase #7	$18.89	8.554%	$20.5059	$20.51	$20.50	$20.50
7 purchase totals =	$923.38		$1,015.2163	$1,015.22	$1,015.25	$1,015.20