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	$238.77	13.467%	$270.9252	$270.93	$270.95	$270.90
Purchase #2	$103.33	10.822%	$114.5124	$114.51	$114.50	$114.50
Purchase #3	$42.47	10.360%	$46.8699	$46.87	$46.85	$46.90
Purchase #4	$83.94	13.445%	$95.2257	$95.23	$95.25	$95.20
Purchase #5	$112.40	12.279%	$126.2016	$126.20	$126.20	$126.20
Purchase #6	$5.55	13.684%	$6.3095	$6.31	$6.30	$6.30
Purchase #7	$59.77	9.659%	$65.5432	$65.54	$65.55	$65.50
7 purchase totals =	$646.23		$725.5875	$725.59	$725.60	$725.50