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	$240.60	6.653%	$256.6071	$256.61	$256.60	$256.60
Purchase #2	$114.47	10.603%	$126.6073	$126.61	$126.60	$126.60
Purchase #3	$27.72	4.282%	$28.907	$28.91	$28.90	$28.90
Purchase #4	$114.55	10.279%	$126.3246	$126.32	$126.30	$126.30
Purchase #5	$102.44	9.793%	$112.4719	$112.47	$112.45	$112.50
Purchase #6	$175.81	9.139%	$191.8773	$191.88	$191.90	$191.90
Purchase #7	$240.63	7.281%	$258.1503	$258.15	$258.15	$258.20
7 purchase totals =	$1,016.22		$1,100.9455	$1,100.95	$1,100.90	$1,101.00