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	$123.37	6.423%	$131.2941	$131.29	$131.30	$131.30
Purchase #2	$25.53	7.780%	$27.5162	$27.52	$27.50	$27.50
Purchase #3	$87.96	3.617%	$91.1415	$91.14	$91.15	$91.10
Purchase #4	$126.46	12.412%	$142.1562	$142.16	$142.15	$142.20
Purchase #5	$98.51	13.510%	$111.8187	$111.82	$111.80	$111.80
Purchase #6	$101.61	5.495%	$107.1935	$107.19	$107.20	$107.20
Purchase #7	$37.95	13.466%	$43.0603	$43.06	$43.05	$43.10
7 purchase totals =	$601.39		$654.1805	$654.18	$654.15	$654.20