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	$49.26	9.742%	$54.0589	$54.06	$54.05	$54.10
Purchase #2	$37.54	3.560%	$38.8764	$38.88	$38.90	$38.90
Purchase #3	$234.90	9.791%	$257.8991	$257.90	$257.90	$257.90
Purchase #4	$86.32	3.574%	$89.4051	$89.41	$89.40	$89.40
Purchase #5	$63.42	7.693%	$68.2989	$68.30	$68.30	$68.30
Purchase #6	$73.77	9.562%	$80.8239	$80.82	$80.80	$80.80
Purchase #7	$234.72	10.797%	$260.0627	$260.06	$260.05	$260.10
7 purchase totals =	$779.93		$849.4250	$849.43	$849.40	$849.50