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	$151.86	5.691%	$160.5024	$160.50	$160.50	$160.50
Purchase #2	$121.42	13.221%	$137.4729	$137.47	$137.45	$137.50
Purchase #3	$103.51	10.555%	$114.4355	$114.44	$114.45	$114.40
Purchase #4	$47.59	5.279%	$50.1023	$50.10	$50.10	$50.10
Purchase #5	$78.89	10.198%	$86.9352	$86.94	$86.95	$86.90
Purchase #6	$169.33	7.241%	$181.5912	$181.59	$181.60	$181.60
Purchase #7	$215.91	4.234%	$225.0516	$225.05	$225.05	$225.10
7 purchase totals =	$888.51		$956.0911	$956.09	$956.10	$956.10