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	$222.65	12.258%	$249.9424	$249.94	$249.95	$249.90
Purchase #2	$84.87	5.416%	$89.4666	$89.47	$89.45	$89.50
Purchase #3	$25.66	7.328%	$27.5404	$27.54	$27.55	$27.50
Purchase #4	$93.30	7.240%	$100.0549	$100.05	$100.05	$100.10
Purchase #5	$107.56	6.818%	$114.8934	$114.89	$114.90	$114.90
Purchase #6	$118.55	5.636%	$125.2315	$125.23	$125.25	$125.20
Purchase #7	$77.94	7.309%	$83.6366	$83.64	$83.65	$83.60
7 purchase totals =	$730.53		$790.7658	$790.76	$790.80	$790.70