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	$25.56	11.751%	$28.5636	$28.56	$28.55	$28.60
Purchase #2	$83.66	9.842%	$91.8938	$91.89	$91.90	$91.90
Purchase #3	$105.56	8.466%	$114.4967	$114.50	$114.50	$114.50
Purchase #4	$171.54	6.441%	$182.5889	$182.59	$182.60	$182.60
Purchase #5	$128.97	10.833%	$142.9413	$142.94	$142.95	$142.90
Purchase #6	$132.68	13.729%	$150.8956	$150.90	$150.90	$150.90
Purchase #7	$50.80	4.767%	$53.2216	$53.22	$53.20	$53.20
7 purchase totals =	$698.77		$764.6015	$764.60	$764.60	$764.60