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	$123.55	11.387%	$137.6186	$137.62	$137.60	$137.60
Purchase #2	$205.82	10.219%	$226.8527	$226.85	$226.85	$226.90
Purchase #3	$63.85	13.453%	$72.4397	$72.44	$72.45	$72.40
Purchase #4	$102.37	10.842%	$113.469	$113.47	$113.45	$113.50
Purchase #5	$28.42	11.108%	$31.5769	$31.58	$31.60	$31.60
Purchase #6	$53.42	7.791%	$57.582	$57.58	$57.60	$57.60
Purchase #7	$64.88	9.314%	$70.9229	$70.92	$70.90	$70.90
7 purchase totals =	$642.31		$710.4618	$710.46	$710.45	$710.50