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	$44.53	9.643%	$48.824	$48.82	$48.80	$48.80
Purchase #2	$180.80	10.620%	$200.001	$200.00	$200.00	$200.00
Purchase #3	$89.82	10.836%	$99.5529	$99.55	$99.55	$99.60
Purchase #4	$13.45	13.631%	$15.2834	$15.28	$15.30	$15.30
Purchase #5	$79.90	5.552%	$84.336	$84.34	$84.35	$84.30
Purchase #6	$109.40	6.804%	$116.8436	$116.84	$116.85	$116.80
Purchase #7	$49.73	6.661%	$53.0425	$53.04	$53.05	$53.00
7 purchase totals =	$567.63		$617.8834	$617.87	$617.90	$617.80