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	$73.72	6.155%	$78.2575	$78.26	$78.25	$78.30
Purchase #2	$225.30	5.291%	$237.2206	$237.22	$237.20	$237.20
Purchase #3	$228.60	11.755%	$255.4719	$255.47	$255.45	$255.50
Purchase #4	$201.81	3.239%	$208.3466	$208.35	$208.35	$208.30
Purchase #5	$201.97	3.417%	$208.8713	$208.87	$208.85	$208.90
Purchase #6	$64.87	10.411%	$71.6236	$71.62	$71.60	$71.60
Purchase #7	$62.68	7.769%	$67.5496	$67.55	$67.55	$67.50
7 purchase totals =	$1,058.95		$1,127.3411	$1,127.34	$1,127.25	$1,127.30