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	$100.59	9.192%	$109.8362	$109.84	$109.85	$109.80
Purchase #2	$215.40	4.867%	$225.8835	$225.88	$225.90	$225.90
Purchase #3	$178.62	6.519%	$190.2642	$190.26	$190.25	$190.30
Purchase #4	$81.88	10.636%	$90.5888	$90.59	$90.60	$90.60
Purchase #5	$165.94	9.270%	$181.3226	$181.32	$181.30	$181.30
Purchase #6	$190.87	13.769%	$217.1509	$217.15	$217.15	$217.20
Purchase #7	$201.45	11.110%	$223.8311	$223.83	$223.85	$223.80
7 purchase totals =	$1,134.75		$1,238.8773	$1,238.87	$1,238.90	$1,238.90