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	$243.78	10.575%	$269.5597	$269.56	$269.55	$269.60
Purchase #2	$127.56	5.630%	$134.7416	$134.74	$134.75	$134.70
Purchase #3	$231.37	10.474%	$255.6037	$255.60	$255.60	$255.60
Purchase #4	$39.29	10.330%	$43.3487	$43.35	$43.35	$43.30
Purchase #5	$102.52	13.662%	$116.5263	$116.53	$116.55	$116.50
Purchase #6	$238.31	7.132%	$255.3063	$255.31	$255.30	$255.30
Purchase #7	$202.97	10.444%	$224.1682	$224.17	$224.15	$224.20
7 purchase totals =	$1,185.80		$1,299.2545	$1,299.26	$1,299.25	$1,299.20