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	$115.64	6.673%	$123.3567	$123.36	$123.35	$123.40
Purchase #2	$134.68	3.594%	$139.5204	$139.52	$139.50	$139.50
Purchase #3	$232.57	12.601%	$261.8761	$261.88	$261.90	$261.90
Purchase #4	$130.93	8.802%	$142.4545	$142.45	$142.45	$142.50
Purchase #5	$9.75	4.541%	$10.1927	$10.19	$10.20	$10.20
Purchase #6	$139.35	6.407%	$148.2782	$148.28	$148.30	$148.30
Purchase #7	$50.75	9.273%	$55.456	$55.46	$55.45	$55.50
7 purchase totals =	$813.67		$881.1346	$881.14	$881.15	$881.30