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	$116.29	10.528%	$128.533	$128.53	$128.55	$128.50
Purchase #2	$74.87	12.394%	$84.1494	$84.15	$84.15	$84.10
Purchase #3	$23.60	11.754%	$26.3739	$26.37	$26.35	$26.40
Purchase #4	$39.41	7.745%	$42.4623	$42.46	$42.45	$42.50
Purchase #5	$238.25	7.124%	$255.2229	$255.22	$255.20	$255.20
Purchase #6	$97.84	5.591%	$103.3102	$103.31	$103.30	$103.30
Purchase #7	$117.46	7.538%	$126.3141	$126.31	$126.30	$126.30
7 purchase totals =	$707.72		$766.3658	$766.35	$766.30	$766.30