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	$107.53	8.430%	$116.5948	$116.59	$116.60	$116.60
Purchase #2	$116.83	11.597%	$130.3788	$130.38	$130.40	$130.40
Purchase #3	$68.97	4.463%	$72.0481	$72.05	$72.05	$72.00
Purchase #4	$176.38	3.806%	$183.093	$183.09	$183.10	$183.10
Purchase #5	$183.46	7.127%	$196.5352	$196.54	$196.55	$196.50
Purchase #6	$65.82	3.440%	$68.0842	$68.08	$68.10	$68.10
Purchase #7	$64.87	9.611%	$71.1047	$71.10	$71.10	$71.10
7 purchase totals =	$783.86		$837.8388	$837.83	$837.90	$837.80